Analytical solution of laminar-laminar stratified two-phase flows with curved interfaces
Brauner, N.; Rovinsky, J.; Maron, D.M.
1995-09-01
The present study represents a complete analytical solution for laminar two-phase flows with curved interfaces. The solution of the Navier-Stokes equations for the two-phases in bipolar coordinates provides the `flow monograms` describe the relation between the interface curvature and the insitu flow geometry when given the phases flow rates and viscosity ratios. Energy considerations are employed to construct the `interface monograms`, whereby the characteristic interfacial curvature is determined in terms of the phases insitu holdup, pipe diameter, surface tension, fluids/wall adhesion and gravitation. The two monograms are then combined to construct the system `operational monogram`. The `operational monogram` enables the determination of the interface configuration, the local flow characteristics, such as velocity profiles, wall and interfacial shear stresses distribution as well as the integral characteristics of the two-phase flow: phases insitu holdup and pressure drop.
Thermal Vibrational Convection in a Two-phase Stratified Liquid
NASA Technical Reports Server (NTRS)
Chang, Qingming; Alexander, J. Iwan D.
2007-01-01
The response of a two-phase stratified liquid system subject to a vibration parallel to an imposed temperature gradient is analyzed using a hybrid thermal lattice Boltzmann method (HTLB). The vibrations considered correspond to sinusoidal translations of a rigid cavity at a fixed frequency. The layers are thermally and mechanically coupled. Interaction between gravity-induced and vibration-induced thermal convection is studied. The ability of applied vibration to enhance the flow, heat transfer and interface distortion is investigated. For the range of conditions investigated, the results reveal that the effect of vibrational Rayleigh number and vibrational frequency on a two-phase stratified fluid system is much different than that for a single-phase fluid system. Comparisons of the response of a two-phase stratified fluid system with a single-phase fluid system are discussed.
Biofluid dynamics of two phase stratified flow through flexible membranes
NASA Astrophysics Data System (ADS)
Bhagavatula Nvssr, Dinesh; Pushpavanam, S.
2016-11-01
Two phase stratified flows between flexible membranes arise in biological flows like lung airway reopening, blood flow in arteries and movement of spinal cord. It is important to understand the physics behind the interaction of flexible membranes and the fluid flow. In this work, a theoretical model is developed and different types of instabilities that arise due to the fluid flow are understood. The solid membrane is modeled as an incompressible linear viscoelastic solid. To simplify the analysis, inertia in the solid is neglected. Linear stability analysis is carried around the base state velocity of the fluid and displacement field of the solid. The flow is perturbed by a small disturbance and a normal mode analysis is carried out to study the growth rate of the disturbance. An eigenvalue problem in formulated using Chebyshev spectral method and is solved to obtain the growth rate of the disturbance. The effect of different parameters such as thickness of the flexible membrane, Reynolds number, viscosity ratio, density ratio, Capillary number and Weissenberg number on the stability characteristics of the flow is studied in detail. Dispersion curves are obtained which explain the stability of the flow. A detail energy analysis is carried out to determine different ways through which energy transfers from the base flow to the disturbed flow.
STUDIES OF TWO-PHASE PLUMES IN STRATIFIED ENVIRONMENTS
Scott A. Socolofsky; Brian C. Crounse; E. Eric Adams
1998-11-18
Two-phase plumes play an important role in the more practical scenarios for ocean sequestration of CO{sub 2}--i.e. dispersing CO{sub 2} as a buoyant liquid from either a bottom-mounted or ship-towed pipeline. Despite much research on related applications, such as for reservoir destratification using bubble plumes, our understanding of these flows is incomplete, especially concerning the phenomenon of plume peeling in a stratified ambient. To address this deficiency, we have built a laboratory facility in which we can make fundamental measurements of plume behavior. Although we are using air, oil and sediments as our sources of buoyancy (rather than CO{sub 2}), by using models, our results can be directly applied to field scale CO{sub 2} releases to help us design better CO{sub 2} injection systems, as well as plan and interpret the results of our up-coming international field experiment. The experimental facility designed to study two-phase plume behavior similar to that of an ocean CO{sub 2} release includes the following components: 1.22 x 1.22 x 2.44 m tall glass walled tank; Tanks and piping for the two-tank stratification method for producing step- and linearly-stratified ambient conditions; Density profiling system using a conductivity and temperature probe mounted to an automated depth profiler; Lighting systems, including a virtual point source light for shadowgraphs and a 6 W argon-ion laser for laser induced fluorescence (LIF) imaging; Imaging system, including a digital, progressive scanning CCD camera, computerized framegrabber, and image acquisition and analysis software; Buoyancy source diffusers having four different air diffusers, two oil diffusers, and a planned sediment diffuser; Dye injection method using a Mariotte bottle and a collar diffuser; and Systems integration software using the Labview graphical programming language and Windows NT. In comparison with previously reported experiments, this system allows us to extend the parameter range of
Stability of stratified two-phase flows in inclined channels
NASA Astrophysics Data System (ADS)
Barmak, I.; Gelfgat, A. Yu.; Ullmann, A.; Brauner, N.
2016-08-01
Linear stability of the stratified gas-liquid and liquid-liquid plane-parallel flows in the inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict the parameter regions in which the stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in the inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of the non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of the steady state solutions are presented on the flow pattern map and are accompanied by the critical wavenumbers and the spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by the streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of two stable stratified flow configurations in a region of low flow rates in the countercurrent liquid-liquid flows. These configurations become unstable with respect to the shear mode of instability. It was revealed that in slightly upward inclined flows the lower and middle solutions for the holdup are stable in the part of the triple solution region, while the upper solution is always unstable. In the case of downward flows, in the triple solution region, none of the solutions are stable with respect to the short-wave perturbations. These flows are stable only in the single solution region at low flow rates of the heavy phase, and the long-wave perturbations are the most unstable ones.
Two-phase air-water stratified flow measurement using ultrasonic techniques
Fan, Shiwei; Yan, Tinghu; Yeung, Hoi
2014-04-11
In this paper, a time resolved ultrasound system was developed for investigating two-phase air-water stratified flow. The hardware of the system includes a pulsed wave transducer, a pulser/receiver, and a digital oscilloscope. The time domain cross correlation method is used to calculate the velocity profile along ultrasonic beam. The system is able to provide velocities with spatial resolution of around 1mm and the temporal resolution of 200μs. Experiments were carried out on single phase water flow and two-phase air-water stratified flow. For single phase water flow, the flow rates from ultrasound system were compared with those from electromagnetic flow (EM) meter, which showed good agreement. Then, the experiments were conducted on two-phase air-water stratified flow and the results were given. Compared with liquid height measurement from conductance probe, it indicated that the measured velocities were explainable.
Robust Risk Prediction with Biomarkers under Two-Phase Stratified Cohort Design
Payne, Rebecca; Yang, Ming; Zheng, Yingye; Jensen, Majken K.; Cai, Tianxi
2016-01-01
Summary Identification of novel biomarkers for risk prediction is important for disease prevention and optimal treatment selection. However, studies aiming to discover which biomarkers are useful for risk prediction often require the use of stored biological samples from large assembled cohorts, and thus the depletion of a finite and precious resource. To make efficient use of such these stored samples, two-phase sampling designs are often adopted as resource-efficient sampling strategies, especially when the outcome of interest is rare. Existing methods for analyzing data from two-phase studies focus primarily on single marker analysis or fitting the Cox regression model to combine information from multiple markers. However, the Cox model may not fit the data well. Under model misspecification, the composite score derived from the Cox model may not perform well in predicting the outcome. Under a general two-phase stratified cohort sampling design, we present a novel approach to combining multiple markers to optimize prediction by fitting a flexible non-parametric transformation model. Using inverse probability weighting to account for the outcome dependent sampling, we propose to estimate the model parameters by maximizing an objective function which can be interpreted as a weighted C-statistic for survival outcomes. Regardless of model adequacy, the proposed procedure yields a sensible composite risk score for prediction. A major obstacle for making inference under two phase studies is due to the correlation induced by the finite population sampling, which prevents standard inference procedures such as the bootstrap from being used for variance estimation. We propose a resampling procedure to derive valid confidence intervals for the model parameters and the C-statistic accuracy measure. We illustrate the new methods with simulation studies and an analysis of a two-phase study of high-density lipoprotein cholesterol (HDL-C) subtypes for predicting the risk of
Robust risk prediction with biomarkers under two-phase stratified cohort design.
Payne, Rebecca; Yang, Ming; Zheng, Yingye; Jensen, Majken K; Cai, Tianxi
2016-12-01
Identification of novel biomarkers for risk prediction is important for disease prevention and optimal treatment selection. However, studies aiming to discover which biomarkers are useful for risk prediction often require the use of stored biological samples from large assembled cohorts, and thus the depletion of a finite and precious resource. To make efficient use of such stored samples, two-phase sampling designs are often adopted as resource-efficient sampling strategies, especially when the outcome of interest is rare. Existing methods for analyzing data from two-phase studies focus primarily on single marker analysis or fitting the Cox regression model to combine information from multiple markers. However, the Cox model may not fit the data well. Under model misspecification, the composite score derived from the Cox model may not perform well in predicting the outcome. Under a general two-phase stratified cohort sampling design, we present a novel approach to combining multiple markers to optimize prediction by fitting a flexible nonparametric transformation model. Using inverse probability weighting to account for the outcome-dependent sampling, we propose to estimate the model parameters by maximizing an objective function which can be interpreted as a weighted C-statistic for survival outcomes. Regardless of model adequacy, the proposed procedure yields a sensible composite risk score for prediction. A major obstacle for making inference under two phase studies is due to the correlation induced by the finite population sampling, which prevents standard inference procedures such as the bootstrap from being used for variance estimation. We propose a resampling procedure to derive valid confidence intervals for the model parameters and the C-statistic accuracy measure. We illustrate the new methods with simulation studies and an analysis of a two-phase study of high-density lipoprotein cholesterol (HDL-C) subtypes for predicting the risk of coronary heart
Garg, P.; Picardo, J. R.; Pushpavanam, S.
2014-07-15
In this work, we investigate the fully developed flow field of two vertically stratified fluids (one phase flowing above the other) in a curved channel of rectangular cross section. The domain perturbation technique is applied to obtain an analytical solution in the asymptotic limit of low Reynolds numbers and small curvature ratios (the ratio of the width of the channel to its radius of curvature). The accuracy of this solution is verified by comparison with numerical simulations of the nonlinear equations. The flow is characterized by helical vortices within each fluid, which are driven by centrifugal forces. The number of vortices and their direction of circulation varies with the parameters of the system (the volume fraction, viscosity ratio, and Reynolds numbers). We identify nine distinct flow patterns and organize the parameter space into corresponding flow regimes. We show that the fully developed interface between the fluids is not horizontal, in general, but is deformed by normal stresses associated with the circulatory flow. The results are especially significant for flows in microchannels, where the Reynolds numbers are small. The mathematical results in this paper include an analytical solution to two coupled biharmonic partial differential equations; these equations arise in two-phase, two-dimensional Stokes flows.
Faccini, J.L.H.; Sampaio, P.A.B. de
2006-07-01
This paper reports numerical and experimental investigation of stratified gas-liquid two-phase flow in horizontal circular pipes. The Reynolds averaged Navier Stokes equations (RANS) with the k-{omega} model for a fully developed stratified gas-liquid two-phase flow are solved by using the finite element method. A smooth and horizontal interface surface is assumed without considering the interfacial waves. The continuity of the shear stress across the interface is enforced with the continuity of the velocity being automatically satisfied by the variational formulation. For each given interface position and longitudinal pressure gradient, an inner iteration loop runs to solve the nonlinear equations. The Newton-Raphson scheme is used to solve the transcendental equations by an outer iteration to determine the interface position and pressure gradient for a given pair of volumetric flow rates. The interface position in a 51.2 mm ID circular pipe was measured experimentally by the ultrasonic pulse-echo technique. The numerical results were also compared with experimental results in a 21 mm ID circular pipe reported by Masala [1]. The good agreement between the numerical and experimental results indicates that the k-{omega} model can be applied for the numerical simulation of stratified gas-liquid two-phase flow. (authors)
Lim, Lam Ghai; Pao, William K. S.; Hamid, Nor Hisham; Tang, Tong Boon
2016-01-01
A 360° twisted helical capacitance sensor was developed for holdup measurement in horizontal two-phase stratified flow. Instead of suppressing nonlinear response, the sensor was optimized in such a way that a ‘sine-like’ function was displayed on top of the linear function. This concept of design had been implemented and verified in both software and hardware. A good agreement was achieved between the finite element model of proposed design and the approximation model (pure sinusoidal function), with a maximum difference of ±1.2%. In addition, the design parameters of the sensor were analysed and investigated. It was found that the error in symmetry of the sinusoidal function could be minimized by adjusting the pitch of helix. The experiments of air-water and oil-water stratified flows were carried out and validated the sinusoidal relationship with a maximum difference of ±1.2% and ±1.3% for the range of water holdup from 0.15 to 0.85. The proposed design concept therefore may pose a promising alternative for the optimization of capacitance sensor design. PMID:27384567
Lim, Lam Ghai; Pao, William K S; Hamid, Nor Hisham; Tang, Tong Boon
2016-07-04
A 360° twisted helical capacitance sensor was developed for holdup measurement in horizontal two-phase stratified flow. Instead of suppressing nonlinear response, the sensor was optimized in such a way that a 'sine-like' function was displayed on top of the linear function. This concept of design had been implemented and verified in both software and hardware. A good agreement was achieved between the finite element model of proposed design and the approximation model (pure sinusoidal function), with a maximum difference of ±1.2%. In addition, the design parameters of the sensor were analysed and investigated. It was found that the error in symmetry of the sinusoidal function could be minimized by adjusting the pitch of helix. The experiments of air-water and oil-water stratified flows were carried out and validated the sinusoidal relationship with a maximum difference of ±1.2% and ±1.3% for the range of water holdup from 0.15 to 0.85. The proposed design concept therefore may pose a promising alternative for the optimization of capacitance sensor design.
Breslow, Norman E.; Lumley, Thomas; Ballantyne, Christie M; Chambless, Lloyd E.; Kulich, Michal
2009-01-01
The case-cohort study involves two-phase sampling: simple random sampling from an infinite super-population at phase one and stratified random sampling from a finite cohort at phase two. Standard analyses of case-cohort data involve solution of inverse probability weighted (IPW) estimating equations, with weights determined by the known phase two sampling fractions. The variance of parameter estimates in (semi)parametric models, including the Cox model, is the sum of two terms: (i) the model based variance of the usual estimates that would be calculated if full data were available for the entire cohort; and (ii) the design based variance from IPW estimation of the unknown cohort total of the efficient influence function (IF) contributions. This second variance component may be reduced by adjusting the sampling weights, either by calibration to known cohort totals of auxiliary variables correlated with the IF contributions or by their estimation using these same auxiliary variables. Both adjustment methods are implemented in the R survey package. We derive the limit laws of coefficients estimated using adjusted weights. The asymptotic results suggest practical methods for construction of auxiliary variables that are evaluated by simulation of case-cohort samples from the National Wilms Tumor Study and by log-linear modeling of case-cohort data from the Atherosclerosis Risk in Communities Study. Although not semiparametric efficient, estimators based on adjusted weights may come close to achieving full efficiency within the class of augmented IPW estimators. PMID:20174455
NASA Astrophysics Data System (ADS)
Kuntoro, Hadiyan Yusuf; Hudaya, Akhmad Zidni; Dinaryanto, Okto; Majid, Akmal Irfan; Deendarlianto
2016-06-01
Due to the importance of the two-phase flow researches for the industrial safety analysis, many researchers developed various methods and techniques to study the two-phase flow phenomena on the industrial cases, such as in the chemical, petroleum and nuclear industries cases. One of the developing methods and techniques is image processing technique. This technique is widely used in the two-phase flow researches due to the non-intrusive capability to process a lot of visualization data which are contain many complexities. Moreover, this technique allows to capture direct-visual information data of the flow which are difficult to be captured by other methods and techniques. The main objective of this paper is to present an improved algorithm of image processing technique from the preceding algorithm for the stratified flow cases. The present algorithm can measure the film thickness (hL) of stratified flow as well as the geometrical properties of the interfacial waves with lower processing time and random-access memory (RAM) usage than the preceding algorithm. Also, the measurement results are aimed to develop a high quality database of stratified flow which is scanty. In the present work, the measurement results had a satisfactory agreement with the previous works.
Galbiati, L.; Andreini, P. )
1992-03-01
In this paper a modification to the model of Taitel and Dukler to include the effect of surface tension in transition between stratified and annular regimes is proposed. The predictions of the modified theory given in this paper are compared with empirical boundaries presented in literature. A good agreement has been found.
An electrical impedance sensor for water level measurements in air-water two-phase stratified flows
NASA Astrophysics Data System (ADS)
Ko, Min Seok; Lee, Sung Yong; Lee, Bo An; Yun, Byong Jo; Kim, Kyung Youn; Kim, Sin
2013-09-01
We report a design of an optimized ring-type impedance sensor for water level measurements in air-water stratified flows through horizontal pipes. The ring-type sensor is optimized in view of the sensor linearity. In order to determine an optimal electrode and gap size of a ring-type sensor which generates a linear relationship between the impedance (resistance and/or reactance) and the water level, systematic numerical calculations are performed, and a ring-type impedance sensor of electrode width-to-diameter ratio 0.25 and gap-to-diameter ratio 0.2 has been selected as optimal. Lab-scale static experiments have been conducted to verify the sensor performance in terms of the linearity. Finally, this proposed sensor is installed in a horizontal loop 40 mm in diameter and roughly 5200 mm in length and measures water levels for various stratified flow conditions. The comparisons of water level measurements between the proposed sensor and the high-speed camera images post-processed by the edge detection scheme show that the maximum deviation in dimensionless water level is roughly 0.037, which corresponds to 1.5 mm over the range 40 mm.
Dynamic simulation of wavy-stratified two-phase flow with the one-dimensional two-fluid model
NASA Astrophysics Data System (ADS)
Fullmer, William D.
The one-dimensional two-fluid model is the basis for the description of the transport of mass, momentum and energy in the thermal-hydraulic codes used for nuclear reactor safety analysis. Unlike other physical transport models, the one-dimensional two-fluid model suffers from the possibility of being ill-posed as an initial-boundary value problem depending on the flow conditions and the relevant physical closure laws. Typically, the ill-posedness is dealt with through either excessive numerical damping or the addition of unphysical closure laws designed for the sole purpose of hyperbolization. Unfortunately both methods eliminate the instability along with the problem of ill-posedness causing the model to undoubtedly lose some of its inherent dynamic capability. In this work, a one-dimensional two-fluid model for horizontal or slightly inclined stratified flow is developed. Higher order physical models that are often neglected, such as surface tension and axial viscous stress, are retained for their short-wavelength stability properties. Characteristic, dispersion and nonlinear analyses are performed to demonstrate that the resulting model is linearly well-posed and nonlinearly well-behaved. While it has been known that higher-order differential terms are able to regularize the short-wavelength problem of ill-posedness without removing the long-wavelength instability, the literature is relatively silent on the consequences of using a model under linearly unstable conditions. Using carefully selected conditions in an idealized infinite domain, it is demonstrated for the first time that the one-dimensional two-fluid model exhibits chaotic behavior in addition to limit cycles and asymptotic stability. The chaotic behavior is a consequence of the long-wavelength linear instability (energy source) the nonlinearity (energy transfer) and the short-wavelength dissipation (energy sink). Since the model is chaotic, solutions exhibit a sensitive dependence on initial
NASA Astrophysics Data System (ADS)
Wiederhold, Andreas; Ebert, Reschad; Resagk, Christian; Research Training Group: "Lorentz Force Velocimetry; Lorentz Force Eddy Current Testing" Team
2016-11-01
We report about the feasibility of Lorentz force velocimetry (LFV) for various flow profiles. LFV is a contactless non-invasive technique to measure flow velocity and has been developed in the last years in our institute. This method is advantageous if the fluid is hot, aggressive or opaque like glass melts or liquid metal flows. The conducted experiments shall prove an increased versatility for industrial applications of this method. For the force measurement we use an electromagnetic force compensation balance. As electrolyte salty water is used with an electrical conductivity in the range of 0.035 which corresponds to tap water up to 20 Sm-1. Because the conductivity is six orders less than that of liquid metals, here the challenging bottleneck is the resolution of the measurement system. The results show only a slight influence in the force signal at symmetric and strongly asymmetric flow profiles. Furthermore we report about the application of LFV to stratified two-phase flows. We show that it is possible to detect interface instabilities, which is important for the dimensioning of liquid metal batteries. Deutsche Forschungsgemeinschaft DFG.
Two-phase visualization at cryogenic temperature
NASA Astrophysics Data System (ADS)
Rousset, Bernard; Chatain, Denis; Beysens, Daniel; Jager, Bernard
2001-05-01
This paper presents two different applications for two-phase visualization at low temperature. In the first application, a CCD video camera located inside vacuum is directly supported by the Pyrex pipe containing a two-phase superfluid flow. In the case of slightly positive slopes in which the flow is co-current but ascending, two different flow patterns have been seen, stratified and intermittent, depending on the vapor mass flow. Experimental investigations from stratified to intermittent flow have been made visually and compared to a code derived from the Taitler/Dukler model. The second application concerns phase transition of hydrogen near critical point (33 K) in zero gravity. The experiments have been performed in a cryostat equipped with a 10 T superconducting coil allowing the gravity compensation for hydrogen. Images of the condensation cell are shifted to the top of the cryostat with a specific cryogenic endoscope because CCD cameras do not work in high magnetic fields. The sample was enlightened with diffuse or parallel (coherent) light using a second endoscope. Images obtained in this apparatus are similar with those obtained in space.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume II. Chapters 6-10)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume III. Chapters 11-14)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume IV. Chapters 15-19)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Two-phase/two-phase heat exchanger analysis
NASA Technical Reports Server (NTRS)
Kim, Rhyn H.
1992-01-01
A capillary pumped loop (CPL) system with a condenser linked to a double two-phase heat exchanger is analyzed numerically to simulate the performance of the system from different starting conditions to a steady state condition based on a simplified model. Results of the investigation are compared with those of similar apparatus available in the Space Station applications of the CPL system with a double two-phase heat exchanger.
NASA Technical Reports Server (NTRS)
Witte, Larry C.
1994-01-01
The development of instrumentation for the support of research in two-phase flow in simulated microgravity conditions was performed. The funds were expended in the development of a technique for characterizing the motion and size distribution of small liquid droplets dispersed in a flowing gas. Phenomena like this occur in both microgravity and normal earth gravity situations inside of conduits that are carrying liquid-vapor mixtures at high flow rates. Some effort to develop a conductance probe for the measurement of liquid film thickness was also expended.
Two-phase viscoelastic jetting
Yu, J-D; Sakai, S.; Sethian, J.A.
2008-12-10
A coupled finite difference algorithm on rectangular grids is developed for viscoelastic ink ejection simulations. The ink is modeled by the Oldroyd-B viscoelastic fluid model. The coupled algorithm seamlessly incorporates several things: (1) a coupled level set-projection method for incompressible immiscible two-phase fluid flows; (2) a higher-order Godunov type algorithm for the convection terms in the momentum and level set equations; (3) a simple first-order upwind algorithm for the convection term in the viscoelastic stress equations; (4) central difference approximations for viscosity, surface tension, and upper-convected derivative terms; and (5) an equivalent circuit model to calculate the inflow pressure (or flow rate) from dynamic voltage.
NASA Technical Reports Server (NTRS)
Wallis, Graham B.
1989-01-01
Some features of two recent approaches of two-phase potential flow are presented. The first approach is based on a set of progressive examples that can be analyzed using common techniques, such as conservation laws, and taken together appear to lead in the direction of a general theory. The second approach is based on variational methods, a classical approach to conservative mechanical systems that has a respectable history of application to single phase flows. This latter approach, exemplified by several recent papers by Geurst, appears generally to be consistent with the former approach, at least in those cases for which it is possible to obtain comparable results. Each approach has a justifiable theoretical base and is self-consistent. Moreover, both approaches appear to give the right prediction for several well-defined situations.
Two phase titanium aluminide alloy
Deevi, Seetharama C.; Liu, C. T.
2001-01-01
A two-phase titanic aluminide alloy having a lamellar microstructure with little intercolony structures. The alloy can include fine particles such as boride particles at colony boundaries and/or grain boundary equiaxed structures. The alloy can include alloying additions such as .ltoreq.10 at % W, Nb and/or Mo. The alloy can be free of Cr, V, Mn, Cu and/or Ni and can include, in atomic %, 45 to 55% Ti, 40 to 50% Al, 1 to 5% Nb, 0.3 to 2% W, up to 1% Mo and 0.1 to 0.3% B. In weight %, the alloy can include 57 to 60% Ti, 30 to 32% Al, 4 to 9% Nb, up to 2% Mo, 2 to 8% W and 0.02 to 0.08% B.
Definition of two-phase flow behaviors for spacecraft design
NASA Technical Reports Server (NTRS)
Reinarts, Thomas R.; Best, Frederick R.; Miller, Katherine M.; Hill, Wayne S.
1991-01-01
Data for complete models of two-phase flow in microgravity are taken from in-flight experiments and applied to an adiabatic flow-regime analysis to study the feasibility of two-phase systems for spacecraft. The data are taken from five in-flight experiments by Hill et al. (1990) in which a two-phase pump circulates a freon mixture and vapor and liquid flow streams are measured. Adiabatic flow regimes are analyzed based on the experimental superficial velocities of liquid and vapor, and comparisons are made with the results of two-phase flow regimes at 1 g. A motion analyzer records the flow characteristics at a rate of 1000 frames/sec, and stratified flow regimes are reported at 1 g. The flow regimes observed under microgravitational conditions are primarily annular and include slug and bubbly-slug regimes. The present data are of interest to the design and analysis of two-phase thermal-management systems for use in space missions.
Overcoming ecologic bias using the two-phase study design.
Wakefield, Jon; Haneuse, Sebastien J-P A
2008-04-15
Ecologic (aggregate) data are widely available and widely utilized in epidemiologic studies. However, ecologic bias, which arises because aggregate data cannot characterize within-group variability in exposure and confounder variables, can only be removed by supplementing ecologic data with individual-level data. Here the authors describe the two-phase study design as a framework for achieving this objective. In phase 1, outcomes are stratified by any combination of area, confounders, and error-prone (or discretized) versions of exposures of interest. Phase 2 data, sampled within each phase 1 stratum, provide accurate measures of exposure and possibly of additional confounders. The phase 1 aggregate-level data provide a high level of statistical power and a cross-classification by which individuals may be efficiently sampled in phase 2. The phase 2 individual-level data then provide a control for ecologic bias by characterizing the within-area variability in exposures and confounders. In this paper, the authors illustrate the two-phase study design by estimating the association between infant mortality and birth weight in several regions of North Carolina for 2000-2004, controlling for gender and race. This example shows that the two-phase design removes ecologic bias and produces gains in efficiency over the use of case-control data alone. The authors discuss the advantages and disadvantages of the approach.
Two-Phase Flow Separator Investigation
The goal of the Two-Phase Flow Separator investigation is to help increase understanding of how to separate gases and liquids in microgravity. Many systems on the space station contain both liquids...
Program calculates two-phase pressure drop
Blackwell, W.W.
1980-11-24
Analysts have developed a program for determining the two-phase pressure drop in piping. Written for the TI-59 programmable calculator used with a PC-100C printer, the program incorporates several unique features: it calculates single-phase as well as two-phase pressure drops, has a 10-20 s execution time, permits the operating data to be changed easily, and includes an option for calculating the estimated surface tension of paraffinic hydrocarbon liquids.
Two-phase flow key to offshore line design
Corteville, J.; Besse, J.; Grouvel, J.M.; Roux, A.
1981-08-10
The aim of the research project is to supply engineers with a good knowledge of two-phase oil and gas flow and the means to predict flow regimes; average pressure drop; average liquid hold-up; and, for slug flow, the volume, frequency, and velocity of slugs. The research group has developed a theoretical stratified flow model based on the equations published by Y. Taitel and A.E. Dukler, J.M. Fitremann, and others. This model considers the gas and the liquid layers independently and takes into account the interaction at the interface. Standard fluid mechanics is applied to each phase. The geometry and the transfer characteristics of the interface are modeled semiempirically. The coefficients are obtained from regression analysis of the experimental data measured in the 6-in. test loop. This model gives the liquid hold-up as well as the pressure drop. 7 refs.
Two phase detonation studies conducted in 1971
NASA Technical Reports Server (NTRS)
Nicholls, J. A.
1972-01-01
A report is presented describing the research conducted on five phases: (1) ignition of fuel drops by a shock wave and passage of a shock wave over a burning drop, (2) the energy release pattern of a two-phase detonation with controlled drop sizes, (3) the attenuation of shock and detonation waves passing over an acoustic liner, (4) experimental and theoretical studies of film detonations, and (5) a simplified analytical model of a rotating two-phase detonation wave in a rocket motor.
Two-phase flow in horizontal pipes
Maeder, P.F.; Michaelides, E.E.; DiPippo, R.
1981-09-01
A method is developed in this paper which calculates the two-phase flow friction factor at any state of the fluid in the pipe. The mixing-length theory was employed for the calculation of the Reynolds stresses in turbulent two-phase flow. The friction factors obtained this way are in good agreement with experimental data. It is clear that the choice of the parameter m, or the density distribution, is rather arbitrary. Careful experimentation is required to refine the analysis given in this study, and in particular to provide guidance in the proper selection of the parameter m.
Condensing, Two-Phase, Contact Heat Exchanger
NASA Technical Reports Server (NTRS)
Cox, R. L.; Oren, J. A.; Sauer, L. W.
1988-01-01
Two-phase heat exchanger continuously separates liquid and vapor phases of working fluid and positions liquid phase for efficient heat transfer. Designed for zero gravity. Principle is adapted to other phase-separation applications; for example, in thermodynamic cycles for solar-energy conversion.
Air-water two-phase flow in a 3-mm horizontal tube
NASA Astrophysics Data System (ADS)
Chen, Ing Youn; Chang, Yu-Juei; Wang, Chi-Chung
2000-01-01
Two-phase flow pattern and friction characteristics for air-water flow in a 3.17 mm smooth tube are reported in this study. The range of air-water mass flux is between 50 to 700 kg/m2.s and gas quality is between 0.0001 to 0.9. The pressure drop data are analyzed using the concept of the two-phase frictional multipliers and the Martinelli parameter. Experimental data show that the two-phase friction multipliers are strongly related to the flow pattern. Taitel & Dukler flow regime map fails to predict the stratified flow pattern data. Their transition lines between annular-wavy and annular-intermittent give fair agreement with data. A modified correlation from Klimenko and Fyodoros criterion is able to distinguish the annular and stratified data. For two-phase flow in small tubes, the effect of surface tension force should be significantly present as compared to gravitational force. The tested empirical frictional correlations couldn't predict the pressure drop in small tubes for various working fluids. It is suggested to correlate a reliable frictional multiplier for small horizontal tubes from a large database of various working fluids, and to develop the flow pattern dependent models for the prediction of two-phase pressure drop in small tubes. .
Daniels, L.
1995-06-01
Gas- and vapor-liquid flows through pipework or equipment often pose major difficulties in both design and operation. Typically, two-phase fluid systems are susceptible to flow instabilities, blockages, and pressure and temperature fluctuations. As a result, gas-liquid flows are avoided whenever possible by separating the two phases into individual streams of nearly homogeneous gas and liquid. However, certain process conditions require or inevitably produce two phases. Examples include condensate-return lines flashing into steam, vapor-liquid feed lines entering distillation columns, and refrigerant-return lines that must maintain a specific vapor-liquid ratio for efficient operation. The thermohydraulic behavior of two-phase systems includes variations in pressure drop, flow patterns, and liquid holdup or void fraction. Increasing the pipe diameter reduces the pressure drop for a given flowrate, or alternatively produces an increase in the flowrate for a given pressure drop in a piping system. However, increased pipeline diameters lead to higher costs, and may require installation of more expensive equipment to accommodate the resulting larger slug volumes. There have been numerous improvements in correlations and methods for the prediction of pressure drop in gas-liquid flows. A few of them attempt to take into account the highly complex flow structure of a two-phase flow. One must keep in mind that the flow structure varies with time and position in the pipework. The paper discusses empirical correlations, pressure drop due to friction, gravity, and acceleration, transitions in flow patterns, liquid inventories, and erosion. 46 refs.
Pressure drop in two-phase flow
NASA Astrophysics Data System (ADS)
Akashah, S. A.
1980-12-01
A computer program was developed containing some of the methods for predicting pressure drop in two-phase flow. The program contains accurate methods for predicting phase behavior and physical properties and can be used to calculate pressure drops for horizontal, inclined and vertical phases. The program was used to solve test cases for many types of flow, varying the diameter, roughness, composition, overall heat transfer coefficient, angle of inclination, and length. The Lockhart-Martinelli correlation predicts the highest pressure drop while the Beggs and Brill method predicts the lowest. The American Gas Association-American Petroleum Institute method is consistent and proved to be reliable in vertical, horizontal and inclined flow. The roughness of the pipe diameter had great effect on pressure drop in two-phase flow, while the overall heat transfer coefficient had little effect.
Apparatus for monitoring two-phase flow
Sheppard, John D.; Tong, Long S.
1977-03-01
A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.
Dynamic failure in two-phase materials
Fensin, S. J.; Walker, E. K.; Cerreta, E. K.; Trujillo, C. P.; Martinez, D. T.; Gray, G. T.
2015-12-21
Previous experimental research has shown that microstructural features such as interfaces, inclusions, vacancies, and heterogeneities can all act as voidnucleation sites. However, it is not well understood how important these interfaces are to damage evolution and failure as a function of the surrounding parentmaterials. In this work, we present results on three different polycrystallinematerials: (1) Cu, (2) Cu-24 wt. %Ag, and (3) Cu-15 wt. %Nb which were studied to probe the influence of bi-metal interfaces onvoidnucleation and growth. These materials were chosen due to the range of difference in structure and bulk properties between the two phases. The initial results suggest that when there are significant differences between the bulk properties (for example: stacking fault energy, melting temperature, etc.) the type of interface between the two parent materials does not principally control the damage nucleation and growth process. Rather, it is the “weaker” material that dictates the dynamic spall strength of the overall two-phase material.
Pumped two-phase heat transfer loop
NASA Technical Reports Server (NTRS)
Edelstein, Fred (Inventor)
1987-01-01
A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes a plurality of independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.
Pumped two-phase heat transfer loop
NASA Technical Reports Server (NTRS)
Edelstein, Fred
1988-01-01
A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes several independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.
Two-phase charge-coupled device
NASA Technical Reports Server (NTRS)
Kosonocky, W. F.; Carnes, J. E.
1973-01-01
A charge-transfer efficiency of 99.99% per stage was achieved in the fat-zero mode of operation of 64- and 128-stage two-phase charge-coupled shift registers at 1.0-MHz clock frequency. The experimental two-phase charge-coupled shift registers were constructed in the form of polysilicon gates overlapped by aluminum gates. The unidirectional signal flow was accomplished by using n-type substrates with 0.5 to 1.0 ohm-cm resistivity in conjunction with a channel oxide thickness of 1000 A for the polysilicon gates and 3000 A for the aluminum gates. The operation of the tested shift registers with fat zero is in good agreement with the free-charge transfer characteristics expected for the tested structures. The charge-transfer losses observed when operating the experimental shift registers without the fat zero are attributed to fast interface state trapping. The analytical part of the report contains a review backed up by an extensive appendix of the free-charge transfer characteristics of CCD's in terms of thermal diffusion, self-induced drift, and fringing field drift. Also, a model was developed for the charge-transfer losses resulting from charge trapping by fast interface states. The proposed model was verified by the operation of the experimental two-phase charge-coupled shift registers.
Critical thinking: a two-phase framework.
Edwards, Sharon L
2007-09-01
This article provides a comprehensive review of how a two-phase framework can promote and engage nurses in the concepts of critical thinking. Nurse education is required to integrate critical thinking in their teaching strategies, as it is widely recognised as an important part of student nurses becoming analytical qualified practitioners. The two-phase framework can be incorporated in the classroom using enquiry-based scenarios or used to investigate situations that arise from practice, for reflection, analysis, theorising or to explore issues. This paper proposes a two-phase framework for incorporation in the classroom and practice to promote critical thinking. Phase 1 attempts to make it easier for nurses to organise and expound often complex and abstract ideas that arise when using critical thinking, identify more than one solution to the problem by using a variety of cues to facilitate action. Phase 2 encourages nurses to be accountable and responsible, to justify a decision, be creative and innovative in implementing change.
Tracking Interfaces in Vertical Two-Phase Flows
Aktas, Birol
2002-07-01
The presence of stratified liquid-gas interfaces in vertical flows poses difficulties to most classes of solution methods for two-phase flows of practical interest in the field of reactor safety and thermal-hydraulics. These difficulties can plague the reactor simulations unless handled with proper care. To illustrate these difficulties, the US NRC Consolidated Thermal-hydraulics Code (TRAC-M) was exercised with selected numerical bench-mark problems. These numerical benchmarks demonstrate that the use of an average void fraction for computational volumes simulating vertical flows is inadequate when these volumes consist of stratified liquid-gas interfaces. In these computational volumes, there are really two regions separated by the liquid-gas interface and each region has a distinct flow topology. An accurate description of these divided computational volumes require that separate void fractions be assigned to each region. This strategy requires that the liquid-gas interfaces be tracked in order to determine their location, the volumes of regions separated by the interface, and the void fractions in these regions. The idea of tracking stratified liquid-gas interfaces is not new. There are examples of tracking methods that were developed for reactor safety codes and applied to reactor simulations in the past with some limited success. The users of these safety codes were warned against potential flow oscillations, conflicting water levels, and pressure disturbances which could be caused by the tracking methods themselves. An example of these methods is the level tracking method of TRAC-M. A review of this method is given here to explore the reasons behind its failures. The review shows that modifications to the field equations are mostly responsible for these failures. Following the review, a systematic approach to incorporate interface tracking methods is outlined. This approach is applicable to most classes of solution methods. For demonstration, the approach to
Numerical Simulation of Two Phase Flows
NASA Technical Reports Server (NTRS)
Liou, Meng-Sing
2001-01-01
Two phase flows can be found in broad situations in nature, biology, and industry devices and can involve diverse and complex mechanisms. While the physical models may be specific for certain situations, the mathematical formulation and numerical treatment for solving the governing equations can be general. Hence, we will require information concerning each individual phase as needed in a single phase. but also the interactions between them. These interaction terms, however, pose additional numerical challenges because they are beyond the basis that we use to construct modern numerical schemes, namely the hyperbolicity of equations. Moreover, due to disparate differences in time scales, fluid compressibility and nonlinearity become acute, further complicating the numerical procedures. In this paper, we will show the ideas and procedure how the AUSM-family schemes are extended for solving two phase flows problems. Specifically, both phases are assumed in thermodynamic equilibrium, namely, the time scales involved in phase interactions are extremely short in comparison with those in fluid speeds and pressure fluctuations. Details of the numerical formulation and issues involved are discussed and the effectiveness of the method are demonstrated for several industrial examples.
Dynamic failure in two-phase materials
Fensin, S. J.; Walker, E. K.; Cerreta, E. K.; ...
2015-12-21
Previous experimental research has shown that microstructural features such as interfaces, inclusions, vacancies, and heterogeneities can all act as voidnucleation sites. However, it is not well understood how important these interfaces are to damage evolution and failure as a function of the surrounding parentmaterials. In this work, we present results on three different polycrystallinematerials: (1) Cu, (2) Cu-24 wt. %Ag, and (3) Cu-15 wt. %Nb which were studied to probe the influence of bi-metal interfaces onvoidnucleation and growth. These materials were chosen due to the range of difference in structure and bulk properties between the two phases. The initial resultsmore » suggest that when there are significant differences between the bulk properties (for example: stacking fault energy, melting temperature, etc.) the type of interface between the two parent materials does not principally control the damage nucleation and growth process. Rather, it is the “weaker” material that dictates the dynamic spall strength of the overall two-phase material.« less
Microgravity Two-Phase Flow Transition
NASA Technical Reports Server (NTRS)
Parang, M.; Chao, D.
1999-01-01
Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.
Stability of oscillatory two phase Couette flow
NASA Technical Reports Server (NTRS)
Coward, Adrian V.; Papageorgiou, Demetrios T.
1993-01-01
We investigate the stability of two phase Couette flow of different liquids bounded between plane parallel plates. One of the plates has a time dependent velocity in its own plane, which is composed of a constant steady part and a time harmonic component. In the absence of time harmonic modulations, the flow can be unstable to an interfacial instability if the viscosities are different and the more viscous fluid occupies the thinner of the two layers. Using Floquet theory, we show analytically in the limit of long waves, that time periodic modulations in the basic flow can have a significant influence on flow stability. In particular, flows which are otherwise unstable for extensive ranges of viscosity ratios, can be stabilized completely by the inclusion of background modulations, a finding that can have useful consequences in many practical applications.
NASA Technical Reports Server (NTRS)
Moerk, J. Steven (Inventor); Youngquist, Robert C. (Inventor); Werlink, Rudy J. (Inventor)
1999-01-01
A quality and/or flow meter employs a capacitance probe assembly for measuring the dielectric constant of flow stream, particularly a two-phase flow stream including liquid and gas components.ne dielectric constant of the flow stream varies depending upon the volume ratios of its liquid and gas components, and capacitance measurements can therefore be employed to calculate the quality of the flow, which is defined as the volume ratio of liquid in the flow to the total volume ratio of gas and liquid in the flow. By using two spaced capacitance sensors, and cross-correlating the time varying capacitance values of each, the velocity of the flow stream can also be determined. A microcontroller-based processing circuit is employed to measure the capacitance of the probe sensors.The circuit employs high speed timer and counter circuits to provide a high resolution measurement of the time interval required to charge each capacitor in the probe assembly. In this manner, a high resolution, noise resistant, digital representation of each of capacitance value is obtained without the need for a high resolution A/D converter, or a high frequency oscillator circuit. One embodiment of the probe assembly employs a capacitor with two ground plates which provide symmetry to insure that accurate measurements are made thereby.
Condensation in a two-phase pool
Duffey, R.B. ); Hughes, E.D. )
1991-01-01
We consider the case of vapor condensation in a liquid pool, when the heat transfer is controlled by heat losses through the walls. The analysis is based on drift flux theory for phase separation in the pool, and determines the two-phase mixture height for the pool. To our knowledge this is the first analytical treatment of this classic problem that gives an explicit result, previous work having established the result for the evaporative case. From conservation of mass and energy in a one-dimensional steady flow, together with a void relation between the liquid and vapor fluxes, we determine the increase in the mixture level from the base level of the pool. It can be seen that the thermal and hydrodynamic influences are separable. Thus, the thermal influence of the wall heat transfer appears through its effect on the condensing length L*, so that at high condensation rates the pool is all liquid, and at low rates overflows (the level swell or foaming effect). Similarly, the phase separation effect hydrodynamically determines the height via the relative velocity of the mixture to the entering flux. We examine some practical applications of this result to level swell in condensing flows, and also examine some limits in ideal cases.
Condensation in a two-phase pool
Duffey, R.B.; Hughes, E.D.
1991-12-31
We consider the case of vapor condensation in a liquid pool, when the heat transfer is controlled by heat losses through the walls. The analysis is based on drift flux theory for phase separation in the pool, and determines the two-phase mixture height for the pool. To our knowledge this is the first analytical treatment of this classic problem that gives an explicit result, previous work having established the result for the evaporative case. From conservation of mass and energy in a one-dimensional steady flow, together with a void relation between the liquid and vapor fluxes, we determine the increase in the mixture level from the base level of the pool. It can be seen that the thermal and hydrodynamic influences are separable. Thus, the thermal influence of the wall heat transfer appears through its effect on the condensing length L*, so that at high condensation rates the pool is all liquid, and at low rates overflows (the level swell or foaming effect). Similarly, the phase separation effect hydrodynamically determines the height via the relative velocity of the mixture to the entering flux. We examine some practical applications of this result to level swell in condensing flows, and also examine some limits in ideal cases.
Two-Phase Nozzle Theory and Parametric Analysis.
1980-06-01
prime-mover applications and for geothermal power generation. The major difference between single-phase (gas) nozzle flow and two-phase nozzle flow is...and the thermophysical properties of the two phases. will increase the enthalpy of the two-phase mixture as well as heat transfer from the droplets to...of the thermal energy of the liquid is transferred efficiently to the gas phase, and the resulting two-phase enthalpy is then converted into kinetic
Bharathan, Desikan; Hassani, Vahab
2008-05-20
A stratified vapor generator (110) comprises a first heating section (H.sub.1) and a second heating section (H.sub.2). The first and second heating sections (H.sub.1, H.sub.2) are arranged so that the inlet of the second heating section (H.sub.2) is operatively associated with the outlet of the first heating section (H.sub.1). A moisture separator (126) having a vapor outlet (164) and a liquid outlet (144) is operatively associated with the outlet (124) of the second heating section (H.sub.2). A cooling section (C.sub.1) is operatively associated with the liquid outlet (144) of the moisture separator (126) and includes an outlet that is operatively associated with the inlet of the second heating section (H.sub.2).
Fluttering in Stratified Flows
NASA Astrophysics Data System (ADS)
Lam, Try; Vincent, Lionel; Kanso, Eva
2016-11-01
The descent motion of heavy objects under the influence of gravitational and aerodynamic forces is relevant to many branches of engineering and science. Examples range from estimating the behavior of re-entry space vehicles to studying the settlement of marine larvae and its influence on underwater ecology. The behavior of regularly shaped objects freely falling in homogeneous fluids is relatively well understood. For example, the complex interaction of a rigid coin with the surrounding fluid will cause it to either fall steadily, flutter, tumble, or be chaotic. Less is known about the effect of density stratification on the descent behavior. Here, we experimentally investigate the descent of discs in both pure water and in a linearly salt-stratified fluids where the density is varied from 1.0 to 1.14 of that of water where the Brunt-Vaisala frequency is 1.7 rad/sec and the Froude number Fr < 1. We found that stratification enhances the radial dispersion of the disc at landing, and simultaneously, decrease the descent speed and the inclination (or nutation) angle while falling. We conclude by commenting on the relevance of these results to the use of unpowered vehicles and robots for space exploration and underwater missions.
A bi-directional two-phase/two-phase heat exchanger
NASA Technical Reports Server (NTRS)
Ku, Jentung; Ottenstein, Laura
1993-01-01
This paper describes the design and test of a heat exchanger that transfers heat from one two-phase thermal loop to another with very small drops in temperature and pressure. The heat exchanger condenses the vapor in one loop while evaporating the liquid in the other without mixing of the condensing and evaporating fluids. The heat exchanger is bidirectional in that it can transfer heat in reverse, condensing on the normally evaporating side and vice versa. It is fully compatible with capillary pumped loops and mechanically pumped loops. Test results verified that performance of the heat exchanger met the design requirements. It demonstrated a heat transfer rate of 6800 watts in the normal mode of operation and 1000 watts in the reverse mode with temperature drops of less than 5 C between two thermal loops.
Next steps in two-phase flow: executive summary
DiPippo, R.
1980-09-01
The executive summary includes the following topics of discussion: the state of affairs; the fundamental governing equations; the one-dimensional mixture model; the drift-flux model; the Denver Research Institute two-phase geothermal flow program; two-phase flow pattern transition criteria; a two-fluid model under development; the mixture model as applied to geothermal well flow; DRI downwell instrumentation; two-phase flow instrumentation; the Sperry Research Corporation downhole pump and gravity-head heat exchanger systems; and the Brown University two-phase flow experimental program. (MHR)
Two-phase flow measurements with advanced instrumented spool pieces
Turnage, K.C.
1980-09-01
A series of two-phase, air-water and steam-water tests performed with instrumented piping spool pieces is described. The behavior of the three-beam densitometer, turbine meter, and drag flowmeter is discussed in terms of two-phase models. Results from application of some two-phase mass flow models to the recorded spool piece data are shown. Results of the study are used to make recommendations regarding spool piece design, instrument selection, and data reduction methods to obtain more accurate measurements of two-phase flow parameters. 13 refs., 23 figs., 1 tab.
Deshpande, S.D.
1985-01-01
Non-Newtonian liquid-gas stratified flow data in 0.026- and 0.052-m-diameter pipes were obtained. Interfacial level gradients between the two phases were observed. The Heywood-Charles model is found to be valid for pseudoplastic liquid-gas uniform stratified flow. Two-phase drag reduction in non-Newtonian systems was not achieved as the transition to semi-slug flow occurred before the model criteria were reached. Interfacial liquid and gas shear stresses were compared. A new parameter ..sigma../sup 2/ is introduced which is a numerical indication of the interfacial level gradient. Two-phase drag reduction was experimentally observed in polymer solution-air plug-slug flow in 0.026- and 0.052-m-diameter pipes. The Hubbard-Dukler pressure drop model was extended to non-Newtonian systems. Reasonable agreement between the experiment and the model predictions is obtained. However, more work needs to be done in order to better understand the two-phase drag reduction phenomena. Liquid holdup correlations were developed for both Newtonian and non-Newtonian systems which successfully correlate the holdup over a wide range of parameters. The Petukhov correlation is found to be better than the Dittus-Boelter correlation in predicting the single-phase water heat-transfer coefficients.
Response of two-phase droplets to intense electromagnetic radiation
NASA Technical Reports Server (NTRS)
Spann, James F.; Maloney, Daniel J.; Lawson, William F.; Casleton, Kent H.
1993-01-01
The behavior of two-phase droplets subjected to high intensity radiation pulses is studied. Droplets are highly absorbing solids in weakly absorbing liquid medium. The objective of the study was to define heating thresholds required for causing explosive boiling and secondary atomization of the fuel droplet. The results point to mechanisms for energy storage and transport in two-phase systems.
Two-Phase Technology at NASA/Johnson Space Center
NASA Technical Reports Server (NTRS)
Ungar, Eugene K.; Nicholson, Leonard S. (Technical Monitor)
1999-01-01
Since the baseline International Space Station (ISS) External Active Thermal Control System (EATCS) was changed from a two-phase mechanically pumped system to a single phase cascade system in the fall of 1993, two-phase EATCS research has continued at a low level at JSC. One of-the lessons of the ISS EATCS selection was that two-phase thermal control systems must have significantly lower power than comparable single phase systems to overcome their larger radiator area, larger line and fluid mass, and perceived higher technical risk. Therefore, research at JSC has concentrated on low power mechanically pumped two-phase EATCSs. In the presentation, the results of a study investigating the trade of single and two-phase mechanically pumped EATCSs for space vehicles will be summarized. The low power two-phase mechanically pumped EATCS system under development at JSC will be described in detail and the current design status of the subscale test unit will be reviewed. Also, performance predictions for a full size EATCS will be presented. In addition to the discussion of two-phase mechanically pumped EATCS development at JSC, two-phase technologies under development for biological water processing will be discussed. These biological water processor technologies are being prepared for a 2001 flight experiment and subsequent usage on the TransHab module on the International Space Station.
Two-phase flow research. Phase I. Two-phase nozzle research. Final report
Toner, S.J.
1981-07-01
An investigation of energy transfer in two-phase nozzles was conducted. Experimental performance of converging-diverging nozzles operating on air-water mixtures is presented for a wide range of parameters. Thrust measurements characterized the performance and photographic documentation was used to visually observe the off-design regimes. Thirty-six nozzle configurations were tested to determine the effects of convergence angle, area ratio, and nozzle length. In addition, the pressure ratio and mass flowrate ratio were varied to experimentally map off-design performance. The test results indicate the effects of wall friction and infer temperature and velocity differences between phases and the effect on nozzle performance. The major conclusions reached were: the slip ratio between the phases, gas velocity to liquid velocity, is shown to be below about 4 or 5, and, in most of the test cases run, was estimated to between about 1-1/2 to 2-1/2; in all cases except the free-jet the mass )
Two-Phase Flow Pressure Drop of High Quality Steam
Curtis, J. M.; Coffield, R. D.
2001-10-01
Two-phase pressure drop across a straight test pipe was experimentally determined for high Reynolds (Re) number steam flow for a flow quality range of 0.995 to 1.0. The testing described has been performed in order to reduce uncertainties associated with the effects of two-phase flow on pressure drop. Two-phase flow develops in steam piping because a small fraction of the steam flow condenses due to heat loss to the surroundings. There has been very limited two-phase pressure drop data in open literature for the tested flow quality range. The two-phase pressure drop data obtained in this test has enabled development of a correlation between friction factor, Reynolds number, and flow quality.
Two-phase-flow models and their limitations
Ishii, M.; Kocamustafaogullari, G.
1982-01-01
An accurate prediction of transient two-phase flow is essential to safety analyses of nuclear reactors under accident conditions. The fluid flow and heat transfer encountered are often extremely complex due to the reactor geometry and occurrence of transient two-phase flow. Recently considerable progresses in understanding and predicting these phenomena have been made by a combination of rigorous model development, advanced computational techniques, and a number of small and large scale supporting experiments. In view of their essential importance, the foundation of various two-phase-flow models and their limitations are discussed in this paper.
Void fraction correlations in two-phase horizontal flow
Papathanassiou, G.; Maeder, P.F.; DiPippo, R.; Dickinson, D.A.
1983-05-01
This study examines some physical mechanisms which impose limits on the possible existence of two-phase flow in a horizontal pipe. With the aid of this analysis and the use of the Martinelli variable, X, a method is developed which determines the range of possible void fractions for a given two-phase flow. This method affords a means of direct comparison among void fraction correlations, as well as between correlation predictions and experimental results. In this respect, four well-known void fraction correlations are compared against each other and with experimental results obtained in the Brown University Two-Phase Flow Research Facility.
What types of investors generate the two-phase phenomenon?
NASA Astrophysics Data System (ADS)
Ryu, Doojin
2013-12-01
We examine the two-phase phenomenon described by Plerou, Gopikrishnan, and Stanley (2003) [1] in the KOSPI 200 options market, one of the most liquid options markets in the world. By analysing a unique intraday dataset that contains information about investor type for each trade and quote, we find that the two-phase phenomenon is generated primarily by domestic individual investors, who are generally considered to be uninformed and noisy traders. In contrast, our empirical results indicate that trades by foreign institutions, who are generally considered informed and sophisticated investors, do not exhibit two-phase behaviour.
Transient two-phase performance of LOFT reactor coolant pumps
Chen, T.H.; Modro, S.M.
1983-01-01
Performance characteristics of Loss-of-Fluid Test (LOFT) reactor coolant pumps under transient two-phase flow conditions were obtained based on the analysis of two large and small break loss-of-coolant experiments conducted at the LOFT facility. Emphasis is placed on the evaluation of the transient two-phase flow effects on the LOFT reactor coolant pump performance during the first quadrant operation. The measured pump characteristics are presented as functions of pump void fraction which was determined based on the measured density. The calculated pump characteristics such as pump head, torque (or hydraulic torque), and efficiency are also determined as functions of pump void fractions. The importance of accurate modeling of the reactor coolant pump performance under two-phase conditions is addressed. The analytical pump model, currently used in most reactor analysis codes to predict transient two-phase pump behavior, is assessed.
Momentum flux in two phase two component low quality flow
NASA Technical Reports Server (NTRS)
Baumeister, K. J.; Graham, R. W.; Henry, R. E.
1972-01-01
In two phase flow systems line losses comprise frictional and momentum pressure drops. For design purposes, it would be desirable to estimate the line losses employing a one-dimensional calculation. Two methods for computing one-dimensional momentum flux at a test section discharge station are compared to the experimental value for a range of two-phase flow conditions. The one-dimensional homogeneous model appears to be more accurate generally in predicting the momentum than the variable slip model.
A jet polishing technique for thinning two phase materials
Witcomb, M.J. ); Dahmen, U. )
1990-11-01
A common problem in the preparation of thin foils for transmission electron microscopy is the different thinning rate in two-phase materials. Often this leads to foils in which the majority, or matrix, phase is evenly polished while the minority, or precipitate, phase is either etched out or stands proud of the surrounding material. In the present report we describe a two-stage jet polishing technique that has been used successfully on different relatively coarse two-phase structures. 3 figs.
Advanced Nanostructures for Two-Phase Fluid and Thermal Transport
2014-08-07
AFRL-OSR-VA-TR-2014-0183 (YIP 11) Advanced Nanostructures for Two-Phase Fluid and Thermal Transport Evelyn Wang MASSACHUSETTS INSTITUTE OF TECHNOLOGY...Advanced Nanostructures for Two-Phase Fluid and Thermal Transport AFOSR Grant FA9550-11-1-0059 Final Report Evelyn N. Wang Associate Professor...heated channel wall. Small fluctuations in the measured heater surface temperature (± 3-8 °C) indicated increased flow stability, and the heat transfer
NASA Astrophysics Data System (ADS)
Kong, Weihang; Li, Lei; Kong, Lingfu; Liu, Xingbin
2016-08-01
In order to solve the problem of dynamic pure-water electrical conductivity measurement in the process of calculating water content of oil-water two-phase flow of production profile logging in horizontal wells, a six-group local-conductance probe (SGLCP) is proposed to measure dynamic pure-water electrical conductivity in horizontal oil-water two-phase flow. The structures of conductance sensors which include the SGLCP and ring-shaped conductance probe (RSCP) are analyzed by using the finite-element method (FEM). In the process of simulation, the electric field distribution generated by the SGLCP and RSCP are investigated, and the responses of the measuring electrodes are calculated under the different values of the water resistivity. The static experiments of the SGLCP and RSCP under different mineralization degrees in horizontal oil-water two-phase flow are carried out. Results of simulation and experiments demonstrate a nice linearity between the SGLCP and RSCP under different mineralization degrees. The SGLCP has also a good adaptability to stratified flow, stratified flow with mixing at the interface and dispersion of oil in water and water flow. The validity and feasibility of pure-water electrical conductivity measurement with the designed SGLCP under different mineralization degrees are verified by experimental results.
Microgravity fluid management in two-phase thermal systems
NASA Technical Reports Server (NTRS)
Parish, Richard C.
1987-01-01
Initial studies have indicated that in comparison to an all liquid single phase system, a two-phase liquid/vapor thermal control system requires significantly lower pumping power, demonstrates more isothermal control characteristics, and allows greater operational flexibility in heat load placement. As a function of JSC's Work Package responsibility for thermal management of space station equipment external to the pressurized modules, prototype development programs were initiated on the Two-Phase Thermal Bus System (TBS) and the Space Erectable Radiator System (SERS). JSC currently has several programs underway to enhance the understanding of two-phase fluid flow characteristics. The objective of one of these programs (sponsored by the Microgravity Science and Applications Division at NASA-Headquarters) is to design, fabricate, and fly a two-phase flow regime mapping experiment in the Shuttle vehicle mid-deck. Another program, sponsored by OAST, involves the testing of a two-phase thermal transport loop aboard the KC-135 reduced gravity aircraft to identify system implications of pressure drop variation as a function of the flow quality and flow regime present in a representative thermal system.
Rotating single cycle two-phase thermally activated heat pump
Fabris, G.
1993-06-08
A thermally activated heat pump is described which utilizes single working fluid which as a whole passes consecutively through all parts of the apparatus in a closed loop series; the working fluid in low temperature saturated liquid state at condensation is pumped to higher pressure with a pump; subsequently heat is added to the liquid of increased pressure, the liquid via the heating is brought to a high temperature saturated liquid state; the high temperature liquid passes and flashes subsequently in form of two-phase flow through a rotating two-phase flow turbine; in such a way the working fluid performs work on the two-phase turbine which in turn powers the liquid pump and a lower compressor; two-phase flow exiting the two-phase turbine separated by impinging tangentially on housing of the turbine; low temperature heat is added to the housing in such a way evaporating the separated liquid on the housing; in such a way the liquid is fully vaporized the vapor then enters a compressor, the compressor compresses the vapor to a higher condensation pressure and corresponding increased temperature, the vapor at the condensation pressure enters a condenser whereby heat is rejected and the vapor is fully condensed into state of saturated liquid, mid saturated liquid enters the pump and repeats the cycle.
Transient well testing in two-phase geothermal reservoirs
Aydelotte, S.R.
1980-03-01
A study of well test analysis techniques in two-phase geothermal reservoirs has been conducted using a three-dimensional, two-phase, wellbore and reservoir simulation model. Well tests from Cerro Prieto and the Hawaiian Geothermal project have been history matched. Using these well tests as a base, the influence of reservoir permeability, porosity, thickness, and heat capacity, along with flow rate and fracturing were studied. Single and two-phase transient well test equations were used to analyze these tests with poor results due to rapidly changing fluid properties and inability to calculate the flowing steam saturation in the reservoir. The injection of cold water into the reservoir does give good data from which formation properties can be calculated.
Acoustic velocities of two-phase mixtures of cryogenic fluids
NASA Technical Reports Server (NTRS)
Griggs, E. I.; Winter, E. R. F.; Schoenhals, R. J.; Hendricks, R. C.
1982-01-01
Calculated values of the acoustic velocity are presented for single-component and two-component, two-phase mixtures. Three different analytic models were employed. For purposes of comparison, all three models were used in making acoustic-velocity calculations for single-component, equivalent bubbly two-phase mixtures (with insoluble gas) of oxygen and helium and hydrogen and helium. In all cases the results are shown graphically so that the effects of variation in quality or void fraction, temperature and pressure are illustrated.
Two Phase Flow and Space-Based Applications
NASA Technical Reports Server (NTRS)
McQuillen, John
1999-01-01
A reduced gravity environment offers the ability to remove the effect of buoyancy on two phase flows whereby density differences that normally would promote relative velocities between the phases and also alter the shape of the interface are removed. However, besides being a potent research tool, there are also many space-based technologies that will either utilize or encounter two-phase flow behavior, and as a consequence, several questions must be addressed. This paper presents some of these technologies missions. Finally, this paper gives a description of web-sites for some funding.
Thermal analysis of two-phase microchannel cooling
Chen, N.C.J.; Felde, D.K.; Yoder, G.L.
1996-09-01
A design calculation has been performed to determine thermal limits in support of an experiment in two-phase microchannel water cooling. Under the operating condition (one atmosphere pressure and 23{degrees}C inlet temperature), the calculation predicts that the experimental channel can withstand a maximum surface temperature of 115{degrees}C and a heat flux up to 975 W/cm{sup 2} without exceeding the critical heat flux limit. The predicted results also indicate that a uniform heat flux along the channel in the two-phase domain can be achieved so that the heat losses from the experimental test section can be calculated in a straightforward manner.
The transient performance of a two-phase fluid reservoir
NASA Technical Reports Server (NTRS)
Chi, Joseph
1989-01-01
Thermal control of future large, high power spacecraft will require a two-phase fluid central bus. The two-phase fluid reservoir is a critical component in the two-phase fluid bus. It both controls the saturation temperature and provides a space for volumetric changes. A dynamic reservoir simulation model does not currently exist, but it is needed to expedite efforts and reduce risk. During 1989 an effort was made to develop a simulation model of the transient performance of a two-phase fluid reservoir. As a beginning, a preliminary model was developed. It is based upon component mathematical models in lumped parametric form and build upon five component mathematical models for calculating dynamic responses of two-phase fluid reservoirs, primary feedback elements, controller commands, heater actuators, and reservoir heaters. As much as possible, the model took advantage of the available SINDA'85/FLUINT thermal/fluid integrator. Additional calculation logic and computer subroutines were developed to complete implementation of the model. The model is capable of simulating dynamic response of an equilibrium two-phase fluid reservoir. Modification of the model to include the liquid/vapor nonequilibrium is required for applications of the model to simulate performance of reservoir in which the liquid and vapor phases of the reservoir fluid are not in equilibrium. In addition, the model in its present form, needs to be refined in several respects. More empirical data are needed to guide the model development. The model may then be used to conduct a full parametric study of two-phase fluid reservoirs. More complexities in two-phaes flow regions in laboratory and flight conditions may have to be considered eventually if empirical data cannot be simulated satisfactorily. System with other components arrangement also need to be simulated if optimization is ever to be attained. The present model does, however, preliminarily demonstrates that such analyses are quite possible
Experimental study on confined two-phase jets
Levy, Y.; Albagli, D. )
1991-09-01
The basic mixing phenomena in confined, coaxial, particle-laden turbulent flows are studied within the scope of ram combustor research activities. Cold-flow experiments in a relatively simple configuration of confined, coaxial two-phase jets provided both qualitative and quantitative insight on the multiphase mixing process. Pressure, tracer gas concentration, and two-phase velocity measurements revealed that unacceptably long ram combustors are needed for complete confined jet mixing. Comparison of the experimental results with a previous numerical simulation displayed a very good agreement, indicating the potential of the experimental facility for validation of computational parametric studies. 38 refs.
Growth of a two-phase finger in eutectics systems.
Boussinot, G; Hüter, C; Brener, E A
2011-02-01
We present a theoretical study of the growth of a two-phase finger in eutectic systems. This pattern was observed experimentally by Akamatsu and Faivre [Phys. Rev. E 61, 3757 (2000)]. We study this two-phase finger using a boundary-integral formulation and we complement our investigation by a phase-field validation of the stability of the pattern. The deviations from the eutectic temperature and from the eutectic concentration provide two independent control parameters, leading to very different patterns depending on their relative importance. We propose scaling laws for the velocity and the different length scales of the pattern.
Two-Phase Model of Combustion in Explosions
Kuhl, A L; Khasainov, B; Bell, J
2006-06-19
A two-phase model for Aluminum particle combustion in explosions is proposed. It combines the gas-dynamic conservation laws for the gas phase with the continuum mechanics laws of multi-phase media, as formulated by Nigmatulin. Inter-phase mass, momentum and energy exchange are prescribed by the Khasainov model. Combustion is specified as material transformations in the Le Chatelier diagram which depicts the locus of thermodynamic states in the internal energy-temperature plane according to Kuhl. Numerical simulations are used to show the evolution of two-phase combustion fields generated by the explosive dissemination of a powdered Al fuel.
A new contactless impedance sensor for void fraction measurement of gas-liquid two-phase flow
NASA Astrophysics Data System (ADS)
Ji, Haifeng; Chang, Ya; Huang, Zhiyao; Wang, Baoliang; Li, Haiqing
2016-12-01
With impedance elimination principle and phase sensitive demodulation (PSD) technique, this work aims to develop a new contactless impedance sensor, which is suitable for the void fraction measurement of gas-liquid two-phase flow. The impedance elimination principle is used to overcome the unfavorable influences of the coupling capacitances, i.e. the capacitive reactances of the coupling capacitances are eliminated by the inductive reactance of an introduced inductor. PSD technique is used to implement the impedance measurement. Unlike the conventional conductance/impedance sensors which use the equivalent conductance (the real part of the impedance) or the amplitude of the impedance of gas-liquid two-phase flow, the new contactless impedance sensor makes full use of the total impedance information of gas-liquid two-phase flow (including the amplitude, the real part and the imaginary part of the impedance, especially the imaginary part) to implement the void fraction measurement. As a preliminary study, to verify the effectiveness of the new contactless impedance sensor, two prototypes (with different inner diameters of 17.0 mm and 22.0 mm) are developed and experiments are carried out. Two typical flow patterns (bubble flow and stratified flow) of gas-liquid two-phase flow are investigated. The experimental results show that the new contactless impedance sensor is successful and effective. Compared with the conventional conductance/impedance sensors, the new contactless impedance sensor can avoid polarization effect and electrochemical erosion effect. The total impedance information is used and the void fraction measurement performance of the new sensor is satisfactory. The experimental results also indicate that the imaginary part of the impedance of gas-liquid two-phase flow is very useful for the void fraction measurement. Making full use of the total impedance information of gas-liquid two-phase flow can effectively improve the void fraction measurement
Heat transfer analysis of two-phase dispersed swirl flow
Chang Ching.
1991-01-01
A thermodynamic nonequilibrium model was developed for a two-phase, vapor and liquid droplet, dispersed swirl flow in a vertical tube with a twisted-tape insert. It takes account of the heat transfer phenomena between two phases, and each phase with solid boundary where a variable heat flux along axial direction is imposed. A numerical method is developed to solve the system of nonlinear differential equations. The local equilibrium conditions of the fluid at the point of critical heat flux (CHF) are chosen as the initial conditions to start the numerical integration to the downstream. Wall temperature, superheat vapor temperature, heat transfer rate from two phases, and velocity distributions of two phases were predicted and analyzed, which were then verified by comparing them with the low wall-superheat heat exchanger experimental data of water-steam in the range of 900.0 {le} G {le} 1,900.0, 2.51 {le} y {le} 7.53, X{sub CHF} {ge} 0.444. Additional parametric studies of the CHF quality, mass flux, and tape-twist ratio are presented. It is found that higher mass flux, lower tape-twist ratio, and low wall-superheat will give a stronger direct wall-droplet interaction and less superheating of vapor.
Low gravity two-phase flow with heat transfer
NASA Technical Reports Server (NTRS)
Antar, Basil N.
1991-01-01
A realistic model for the transfer line chilldown operation under low-gravity conditions is developed to provide a comprehensive predictive capability on the behavior of liquid vapor, two-phase diabatic flows in pipes. The tasks described involve the development of numerical code and the establishment of the necessary experimental data base for low-gravity simulation.
Two-phase flow in helical and spiral coils
NASA Technical Reports Server (NTRS)
Keshock, Edward G.; Bush, Mia L.; Omrani, Adel; Yan, An
1995-01-01
Coiled tube heat exchangers involving two-phase flows are used in a variety of application areas, extending from the aerospace industry to petrochemical, refrigeration land power generation industries. The optimal design in each situation requires a fundamental understanding of the heat, mass and momentum transfer characteristic of the flowing two-phase mixture. However, two-phase flows in lengths of horizontal or vertical straight channels with heat transfer are often quite difficult in themselves to understand sufficiently well to permit accurate system designs. The present study has the following general objectives: (1) Observe two-phase flow patterns of air-water and R-113 working fluids over a range of flow conditions, for helical and spiral coil geometries, of circular and rectangular cross-section; (2) Compare observed flow patterns with predictions of existing flow maps; (3) Study criteria for flow regime transitions for possible modifications of existing flow pattern maps; and (4) Measure associated pressure drops across the coiled test sections over the rage of flow conditions specified.
Experimental Investigation of two-phase nitrogen Cryo transfer line
NASA Astrophysics Data System (ADS)
Singh, G. K.; Nimavat, H.; Panchal, R.; Garg, A.; Srikanth, GLN; Patel, K.; Shah, P.; Tanna, V. L.; Pradhan, S.
2017-02-01
A 6-m long liquid nitrogen based cryo transfer line has been designed, developed and tested at IPR. The test objectives include the thermo-hydraulic characteristics of Cryo transfer line under single phase as well as two phase flow conditions. It is always easy in experimentation to investigate the thermo-hydraulic parameters in case of single phase flow of cryogen but it is real challenge when one deals with the two phase flow of cryogen due to availibity of mass flow measurements (direct) under two phase flow conditions. Established models have been reported in the literature where one of the well-known model of Lockhart-Martenelli relationship has been used to determine the value of quality at the outlet of Cryo transfer line. Under homogenous flow conditions, by taking the ratio of the single-phase pressure drop and the two-phase pressure drop, we estimated the quality at the outlet. Based on these equations, vapor quality at the outlet of the transfer line was predicted at different heat loads. Experimental rresults shown that from inlet to outlet, there is a considerable increment in the pressure drop and vapour quality of the outlet depending upon heat load and mass flow rate of nitrogen flowing through the line.
Power production with two-phase expansion through vapor dome
Amend, W.E.; Toner, S.J.
1984-08-07
In a system wherein a fluid exhibits a regressive vapor dome in a T-S diagram, the following are provided: a two-phase nozzle receiving the fluid in pressurized and heated liquid state and expanding the received liquid into saturated or superheated vapor state, and apparatus receiving the saturated or superheated vapor to convert the kinetic energy thereof into power.
Coal-Face Fracture With A Two-Phase Liquid
NASA Technical Reports Server (NTRS)
Collins, E. R., Jr.
1985-01-01
In new method for mining coal without explosive, two-phase liquid such as CO2 and water, injected at high pressure into deeper ends of holes drilled in coal face. Liquid permeates coal seam through existing microfractures; as liquid seeps back toward face, pressure eventually drops below critical value at which dissolved gas flashvaporizes, breaking up coal.
A New Void Fraction Measurement Method for Gas-Liquid Two-Phase Flow in Small Channels.
Li, Huajun; Ji, Haifeng; Huang, Zhiyao; Wang, Baoliang; Li, Haiqing; Wu, Guohua
2016-01-27
Based on a laser diode, a 12 × 6 photodiode array sensor, and machine learning techniques, a new void fraction measurement method for gas-liquid two-phase flow in small channels is proposed. To overcome the influence of flow pattern on the void fraction measurement, the flow pattern of the two-phase flow is firstly identified by Fisher Discriminant Analysis (FDA). Then, according to the identification result, a relevant void fraction measurement model which is developed by Support Vector Machine (SVM) is selected to implement the void fraction measurement. A void fraction measurement system for the two-phase flow is developed and experiments are carried out in four different small channels. Four typical flow patterns (including bubble flow, slug flow, stratified flow and annular flow) are investigated. The experimental results show that the development of the measurement system is successful. The proposed void fraction measurement method is effective and the void fraction measurement accuracy is satisfactory. Compared with the conventional laser measurement systems using standard laser sources, the developed measurement system has the advantages of low cost and simple structure. Compared with the conventional void fraction measurement methods, the proposed method overcomes the influence of flow pattern on the void fraction measurement. This work also provides a good example of using low-cost laser diode as a competent replacement of the expensive standard laser source and hence implementing the parameter measurement of gas-liquid two-phase flow. The research results can be a useful reference for other researchers' works.
Studies on Normal and Microgravity Annular Two Phase Flows
NASA Technical Reports Server (NTRS)
Balakotaiah, V.; Jayawardena, S. S.; Nguyen, L. T.
1999-01-01
Two-phase gas-liquid flows occur in a wide variety of situations. In addition to normal gravity applications, such flows may occur in space operations such as active thermal control systems, power cycles, and storage and transfer of cryogenic fluids. Various flow patterns exhibiting characteristic spatial and temporal distribution of the two phases are observed in two-phase flows. The magnitude and orientation of gravity with respect to the flow has a strong impact on the flow patterns observed and on their boundaries. The identification of the flow pattern of a flow is somewhat subjective. The same two-phase flow (especially near a flow pattern transition boundary) may be categorized differently by different researchers. Two-phase flow patterns are somewhat simplified in microgravity, where only three flow patterns (bubble, slug and annular) have been observed. Annular flow is obtained for a wide range of gas and liquid flow rates, and it is expected to occur in many situations under microgravity conditions. Slug flow needs to be avoided, because vibrations caused by slugs result in unwanted accelerations. Therefore, it is important to be able to accurately predict the flow pattern which exists under given operating conditions. It is known that the wavy liquid film in annular flow has a profound influence on the transfer of momentum and heat between the phases. Thus, an understanding of the characteristics of the wavy film is essential for developing accurate correlations. In this work, we review our recent results on flow pattern transitions and wavy films in microgravity.
Two-phase convective CO2 dissolution in saline aquifers
Martinez, Mario J.; Hesse, Marc A.
2016-01-30
Geologic carbon storage in deep saline aquifers is a promising technology for reducing anthropogenic emissions into the atmosphere. Dissolution of injected CO2 into resident brines is one of the primary trapping mechanisms generally considered necessary to provide long-term storage security. Given that diffusion of CO2 in brine is woefully slow, convective dissolution, driven by a small increase in brine density with CO2 saturation, is considered to be the primary mechanism of dissolution trapping. Previous studies of convective dissolution have typically only considered the convective process in the single-phase region below the capillary transition zone and have either ignored the overlyingmore » two-phase region where dissolution actually takes place or replaced it with a virtual region with reduced or enhanced constant permeability. Our objective is to improve estimates of the long-term dissolution flux of CO2 into brine by including the capillary transition zone in two-phase model simulations. In the fully two-phase model, there is a capillary transition zone above the brine-saturated region over which the brine saturation decreases with increasing elevation. Our two-phase simulations show that the dissolution flux obtained by assuming a brine-saturated, single-phase porous region with a closed upper boundary is recovered in the limit of vanishing entry pressure and capillary transition zone. For typical finite entry pressures and capillary transition zone, however, convection currents penetrate into the two-phase region. As a result, this removes the mass transfer limitation of the diffusive boundary layer and enhances the convective dissolution flux of CO2 more than 3 times above the rate assuming single-phase conditions.« less
Two-phase convective CO2 dissolution in saline aquifers
NASA Astrophysics Data System (ADS)
Martinez, M. J.; Hesse, M. A.
2016-01-01
Geologic carbon storage in deep saline aquifers is a promising technology for reducing anthropogenic emissions into the atmosphere. Dissolution of injected CO2 into resident brines is one of the primary trapping mechanisms generally considered necessary to provide long-term storage security. Given that diffusion of CO2 in brine is woefully slow, convective dissolution, driven by a small increase in brine density with CO2 saturation, is considered to be the primary mechanism of dissolution trapping. Previous studies of convective dissolution have typically only considered the convective process in the single-phase region below the capillary transition zone and have either ignored the overlying two-phase region where dissolution actually takes place or replaced it with a virtual region with reduced or enhanced constant permeability. Our objective is to improve estimates of the long-term dissolution flux of CO2 into brine by including the capillary transition zone in two-phase model simulations. In the fully two-phase model, there is a capillary transition zone above the brine-saturated region over which the brine saturation decreases with increasing elevation. Our two-phase simulations show that the dissolution flux obtained by assuming a brine-saturated, single-phase porous region with a closed upper boundary is recovered in the limit of vanishing entry pressure and capillary transition zone. For typical finite entry pressures and capillary transition zone, however, convection currents penetrate into the two-phase region. This removes the mass transfer limitation of the diffusive boundary layer and enhances the convective dissolution flux of CO2 more than 3 times above the rate assuming single-phase conditions.
Investigations of two-phase flame propagation under microgravity conditions
NASA Astrophysics Data System (ADS)
Gokalp, Iskender
2016-07-01
Investigations of two-phase flame propagation under microgravity conditions R. Thimothée, C. Chauveau, F. Halter, I Gökalp Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France This paper presents and discusses recent results on two-phase flame propagation experiments we carried out with mono-sized ethanol droplet aerosols under microgravity conditions. Fundamental studies on the flame propagation in fuel droplet clouds or sprays are essential for a better understanding of the combustion processes in many practical applications including internal combustion engines for cars, modern aircraft and liquid rocket engines. Compared to homogeneous gas phase combustion, the presence of a liquid phase considerably complicates the physico-chemical processes that make up combustion phenomena by coupling liquid atomization, droplet vaporization, mixing and heterogeneous combustion processes giving rise to various combustion regimes where ignition problems and flame instabilities become crucial to understand and control. Almost all applications of spray combustion occur under high pressure conditions. When a high pressure two-phase flame propagation is investigated under normal gravity conditions, sedimentation effects and strong buoyancy flows complicate the picture by inducing additional phenomena and obscuring the proper effect of the presence of the liquid droplets on flame propagation compared to gas phase flame propagation. Conducting such experiments under reduced gravity conditions is therefore helpful for the fundamental understanding of two-phase combustion. We are considering spherically propagating two-phase flames where the fuel aerosol is generated from a gaseous air-fuel mixture using the condensation technique of expansion cooling, based on the Wilson cloud chamber principle. This technique is widely recognized to create well-defined mono-size droplets
Numerical investigations of small diameter two-phase closed thermosyphon
NASA Astrophysics Data System (ADS)
Naresh, Y.; Balaji, C.
2016-09-01
In this work, a CFD model is developed to simulate the working of a 6mm diameter two-phase closed thermosyphon using water as the working fluid. At each section (evaporator, condenser, adiabatic) of the thermosyphon, lumped equations have been developed to calculate the temperatures at corresponding sections. In order to process two phase flow inside the system, a user-defined function (UDF) has been developed and integrated with the CFD model. The volume of fluid (VOF) method is used to carry out the simulations in Ansys FLUENT 15 and the lumped equations are solved in MATLAB 2013a. Volume fractions and temperature profiles obtained from CFD simulations and the lumped parametric estimations are found to be in good agreement with the experimental results available in literature.
Two-phase flows in solid rocket motors
NASA Astrophysics Data System (ADS)
Murakami, Takuji; Shimada, Toru
Axisymmetric gas-particle two-phase flows in solid-rocket-motor combustion chambers and nozzles with small throat radius of curvature and with submerged configuration are investigated numerically by utilizing a second-order finite-volume method with van Leer's flux-vector splitting in conjunction with a technique of body-fitted cell system. Effects of the particle radius and the particle mass fraction on the two-phase flow, especially on the particle density distribution, the particle-free zone, and the rate of deceleration of the gas are studied. The scheme can capture the particle-free zone with a relatively coarse cell system without numerical oscillation, being benefited by internal dissipative effect which this high-resolution upwind method involves. The validity of the present numerical simulation is thus confirmed.
Two-phase flow regime map predictions under microgravity
Karri, S.B.R.; Mathur, V.K.
1988-01-01
In this paper, the widely used models of Taitel-Dukler and Weisman et al. are extrapolated to microgravity levels to compare predicted flow pattern boundaries for horizontal and vertical flows. Efforts have been made to analyze how the two-phase flow models available in the literature predict flow regime transitions in microgravity. The models of Taitel-Dukler and Weisman et al. have been found to be more suitable for extrapolation to a wide range of system parameters than the other two-phase flow regime maps available in the literature. The original criteria for all cases are used to predict the transition lines, except for the transition to dispersed flow regime in case of the Weisman model for horizontal flow. The constant 0.97 on the righthand side of this correlation should be two times that value, i.e., 1.94, in order to match this transition line in their original paper.
Convective heat transfer in a closed two-phase thermosyphon
NASA Astrophysics Data System (ADS)
Al-Ani, M. A.
2014-08-01
A numerical analysis of heat transfer processes and hydrodynamics in a two-phase closed thermosyphon in a fairly wide range of variation of governing parameters has been investigated. A mathematical model is formulated based on the laws of mass conservation, momentum and energy in dimensionless variables "stream function - vorticity vector velocity - temperature". The analysis of the modes of forced and mixed convection for different values of Reynolds number and heat flows in the evaporation zone, the possibility of using two-phase thermosyphon for cooling gas turbine blades, when the heat is coming from the turbine blades to the thermosyphon is recycled a secondary refrigerant has been studied with different values of the centrifugal velocity. Nusselet Number, streamlines, velocity, temperature fields and temperature profile has been calculated during the investigation.
Energy efficient two-phase cooling for concentrated photovoltaic arrays
NASA Astrophysics Data System (ADS)
Reeser, Alexander Douglas
Concentrated sunlight focused on the aperture of a photovoltaic solar cell, coupled with high efficiency, triple junction cells can produce much greater power densities than traditional 1 sun photovoltaic cells. However, the large concentration ratios will lead to very high cell temperatures if not efficiently cooled by a thermal management system. Two phase, flow boiling is an attractive cooling option for such CPV arrays. In this work, two phase flow boiling in mini/microchannels and micro pin fin arrays will be explored as a possible CPV cooling technique. The most energy efficient microchannel design is chosen based on a least-material, least-energy analysis. Heat transfer and pressure drop obtained in micro pin fins will be compared to data in the recent literature and new correlations for heat transfer coefficient and pressure drop will be presented. The work concludes with an energy efficiency comparison of micro pin fins with geometrically similar microchannel geometry.
Method and apparatus for monitoring two-phase flow. [PWR
Sheppard, J.D.; Tong, L.S.
1975-12-19
A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.
Theory and Tests of Two-Phase Turbines
NASA Technical Reports Server (NTRS)
Elliott, D. G.
1986-01-01
New turbines open possibility of new types of power cycles. Report describes theoretical analysis and experimental testing of two-phase impulse turbines. Such turbines open possibility of new types of power cycles operating with extremely wet mixtures of steam and water, organic fluids, or immiscible liquids and gases. Possible applications are geothermal power, waste-heat recovery, refrigerant expansion, solar conversion, transportation, and engine-bottoming cycles.
Two-fluid model for two-phase flow
Ishii, M.
1987-01-01
The two-fluid model formulation is discussed in detail. The emphasis of the paper is on the three-dimensional formulation and the closure issues. The origin of the interfacial and turbulent transfer terms in the averaged formulation is explained and their original mathematical forms are examined. The interfacial transfer of mass, momentum, and energy is proportional to the interfacial area and driving force. This is not a postulate but a result of the careful examination of the mathematical form of the exact interfacial terms. These two effects are considered separately. Since all the interfacial transfer terms involve the interfacial area concentration, the accurate modeling of the local interfacial area concentration is the first step to be taken for a development of a reliable two-fluid model closure relations. The interfacial momentum interaction has been studied in terms of the standard-drag, lift, virtual mass, and Basset forces. Available analytical and semi-empirical correlations and closure relations are reviewed and existing shortcomings are pointed out. The other major area of importance is the modeling of turbulent transfer in two-phase flow. The two-phase flow turbulence problem is coupled with the phase separation problem even in a steady-state fully developed flow. Thus the two-phase turbulence cannot be understood without understanding the interfacial drag and lift forces accurately. There are some indications that the mixing length type model may not be sufficient to describe the three-dimensional turbulent and flow structures. Although it is a very difficult challenge, the two-phase flow turbulence should be investigated both experimentally and analytically with long time-scale research. 87 refs.
Recent advances in two-phase flow numerics
Mahaffy, J.H.; Macian, R.
1997-07-01
The authors review three topics in the broad field of numerical methods that may be of interest to individuals modeling two-phase flow in nuclear power plants. The first topic is iterative solution of linear equations created during the solution of finite volume equations. The second is numerical tracking of macroscopic liquid interfaces. The final area surveyed is the use of higher spatial difference techniques.
An experimental investigation of two-phase liquid oxygen pumping
NASA Technical Reports Server (NTRS)
Gross, L. A.
1973-01-01
The results of an experimental program to explore the feasibility of pumping two-phase oxygen (liquid and gas) at the pump inlet are reported. Twenty-one cavitation tests were run on a standard J-2 oxygen pump at the MSFC Components Test Laboratory. All tests were run with liquid oxygen 5 to 10 K above the normal boiling point temperature. During ten tests run at approximately at the pump inlet were noted before complete pump performance 50 percent of the nominal operating speed, two phase conditions were achieved. Vapor volumes of 40 to 50 percent at the pump inlet were noted before complete pump performance loss. The experimental results compared to predictions. Nine cavitation tests run at the nominal pump speed over a 5 K temperature range showed progressively lower net positive suction head (NPSH) requirements as temperature was increased. Two-phase operation was not achieved. The temperature varying NPSH data were used to calculate thermodynamic effects on NPSH, and the results were compared to existing data.
Two-Phase Flow Hydrodynamics in Superhydrophobic Channels
NASA Astrophysics Data System (ADS)
Stevens, Kimberly; Crockett, Julie; Maynes, Daniel; Iverson, Brian
2016-11-01
Superhydrophobic surfaces have been shown to reduce drag in single-phase channel flow; however, little work has been done to characterize the drag reduction found in two-phase channel flow. Adiabatic, air-water mixtures were used to gain insight into the effect of hydrophobicity on two-phase flows and the hydrodynamics which might be present in flow condensation. Pressure drop in a parallel plate channel with one superhydrophobic wall (cross-section 0.5 x 10 mm) and a transparent hydrophilic wall were explored. Data for air/water mixtures with superficial Reynolds numbers from 20-215 and 50-210, respectively, were obtained for superhydrophobic surfaces with three different cavity fractions. Agreement between experimentally obtained two-phase pressure drops and correlations in the literature for conventional smooth control surfaces was better than 20 percent. The reduction in pressure drop for channels with a single superhydrophobic wall were found to be more significant than that for single phase flow. The effect of cavity fraction on drag reduction was within experimental error.
Estimating disease prevalence in two-phase studies.
Alonzo, Todd A; Pepe, Margaret Sullivan; Lumley, Thomas
2003-04-01
Disease prevalence is ideally estimated using a 'gold standard' to ascertain true disease status on all subjects in a population of interest. In practice, however, the gold standard may be too costly or invasive to be applied to all subjects, in which case a two-phase design is often employed. Phase 1 data consisting of inexpensive and non-invasive screening tests on all study subjects are used to determine the subjects that receive the gold standard in the second phase. Naive estimates of prevalence in two-phase studies can be biased (verification bias). Imputation and re-weighting estimators are often used to avoid this bias. We contrast the forms and attributes of the various prevalence estimators. Distribution theory and simulation studies are used to investigate their bias and efficiency. We conclude that the semiparametric efficient approach is the preferred method for prevalence estimation in two-phase studies. It is more robust and comparable in its efficiency to imputation and other re-weighting estimators. It is also easy to implement. We use this approach to examine the prevalence of depression in adolescents with data from the Great Smoky Mountain Study.
Multiparticle imaging technique for two-phase fluid flows using pulsed laser speckle velocimetry
Hassan, T.A.
1992-12-01
The practical use of Pulsed Laser Velocimetry (PLV) requires the use of fast, reliable computer-based methods for tracking numerous particles suspended in a fluid flow. Two methods for performing tracking are presented. One method tracks a particle through multiple sequential images (minimum of four required) by prediction and verification of particle displacement and direction. The other method, requiring only two sequential images uses a dynamic, binary, spatial, cross-correlation technique. The algorithms are tested on computer-generated synthetic data and experimental data which was obtained with traditional PLV methods. This allowed error analysis and testing of the algorithms on real engineering flows. A novel method is proposed which eliminates tedious, undersirable, manual, operator assistance in removing erroneous vectors. This method uses an iterative process involving an interpolated field produced from the most reliable vectors. Methods are developed to allow fast analysis and presentation of sets of PLV image data. Experimental investigation of a two-phase, horizontal, stratified, flow regime was performed to determine the interface drag force, and correspondingly, the drag coefficient. A horizontal, stratified flow test facility using water and air was constructed to allow interface shear measurements with PLV techniques. The experimentally obtained local drag measurements were compared with theoretical results given by conventional interfacial drag theory. Close agreement was shown when local conditions near the interface were similar to space-averaged conditions. However, theory based on macroscopic, space-averaged flow behavior was shown to give incorrect results if the local gas velocity near the interface as unstable, transient, and dissimilar from the average gas velocity through the test facility.
Measurement of Two-Phase Flow Characteristics Under Microgravity Conditions
NASA Technical Reports Server (NTRS)
Keshock, E. G.; Lin, C. S.; Edwards, L. G.; Knapp, J.; Harrison, M. E.; Xhang, X.
1999-01-01
This paper describes the technical approach and initial results of a test program for studying two-phase annular flow under the simulated microgravity conditions of KC-135 aircraft flights. A helical coil flow channel orientation was utilized in order to circumvent the restrictions normally associated with drop tower or aircraft flight tests with respect to two-phase flow, namely spatial restrictions preventing channel lengths of sufficient size to accurately measure pressure drops. Additionally, the helical coil geometry is of interest in itself, considering that operating in a microgravity environment vastly simplifies the two-phase flows occurring in coiled flow channels under 1-g conditions for virtually any orientation. Pressure drop measurements were made across four stainless steel coil test sections, having a range of inside tube diameters (0.95 to 1.9 cm), coil diameters (25 - 50 cm), and length-to-diameter ratios (380 - 720). High-speed video photographic flow observations were made in the transparent straight sections immediately preceding and following the coil test sections. A transparent coil of tygon tubing of 1.9 cm inside diameter was also used to obtain flow visualization information within the coil itself. Initial test data has been obtained from one set of KC-135 flight tests, along with benchmark ground tests. Preliminary results appear to indicate that accurate pressure drop data is obtainable using a helical coil geometry that may be related to straight channel flow behavior. Also, video photographic results appear to indicate that the observed slug-annular flow regime transitions agree quite reasonably with the Dukler microgravity map.
Two-phase methane fermentation of municipal-industrial sludge
Ghosh, S.; Sajjad, A.
1984-01-01
This paper presents the development of an innovative two-phase methane fermentation process that provided a mesophilic methane yield of about 0.5 SCM/kg VS (8 SCF/lb VS) added from digestion of a municipal-industrial sludge at a system hydraulic residence time (HRT) of about 6 days compared with a yield of 0.22 to 0.31 SCM/kg VS (3.5 to 5.0 SCF/lb VS) added obtained from single-stage conventional high-rate digesters operated at HRT's of 10 to 20 days. This innovative process has substantive beneficial impact on the production of net energy and availability of surplus digester methane for sale or conversion to such other energy forms as substitute natural gas, electric power, hot water, or low-pressure steam. The research was conducted with a high-metal-content and difficult-to-treat primary sludge from the South Essex Sewerage District (SESD) water pollution control plant, Salem, Massachusetts. Wastewaters received at the plant include 40 to 60 vol % industrial wastes, the remainder being residential liquid wastes. Incineration, which was the sludge disposal process at the plant, is now unacceptable because it leads to the production of hexavalent chromium and other oxidized metals, and the incinerator ash containing these materials cannot be landfilled. The two-phase process does not generate oxidized species such as Cr/sup 6 +/, produces renewable energy and a highly stabilized residue, and could be an answer to the sludge disposal problems of SESD or other sewage districts. Results of bench-scale process development work are presented here. Design and operation of a 7500 L/day (2000 gal/day) two-phase pilot plant will be started this year with support from the above industrial sponsors and other governmental and public agencies. 6 references, 1 figure, 5 tables.
Centrifugal inertia effects in two-phase face seal films
NASA Technical Reports Server (NTRS)
Basu, P.; Hughes, W. F.; Beeler, R. M.
1987-01-01
A simplified, semianalytical model has been developed to analyze the effect of centrifugal inertia in two-phase face seals. The model is based on the assumption of isothermal flow through the seal, but at an elevated temperature, and takes into account heat transfer and boiling. Using this model, seal performance curves are obtained with water as the working fluid. It is shown that the centrifugal inertia of the fluid reduces the load-carrying capacity dramatically at high speeds and that operational instability exists under certain conditions. While an all-liquid seal may be starved at speeds higher than a 'critical' value, leakage always occurs under boiling conditions.
A real two-phase submarine debris flow and tsunami
NASA Astrophysics Data System (ADS)
Pudasaini, Shiva P.; Miller, Stephen A.
2012-09-01
The general two-phase debris flow model proposed by Pudasaini [1] is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
Similarity considerations in one-component two-phase flow
Maeder, P.F.; DiPippo, R.; Dickinson, D.A.; Nikitopoulos, D.E.
1984-07-01
The simplified model fluid presented here for two-phase flow can serve as a basis for the similarity analysis of a variety of substance flows. For the special case of water and R114, it is seen that exact similarity does not exist in the range of interest for geothermal applications, but that conditions can be found for reasonable similarity which permit one to replace water with R114 in laboratory-size apparatus. Thus experimental data and results obtained using R114 in a properly scaled laboratory setup can be converted with reasonable accuracy to those for water.
Neutron Imaging of a Two-Phase Refrigerant Flow
Geoghegan, Patrick J
2015-01-01
Void fraction remains a crucial parameter in understanding and characterizing two-phase flow. It appears as a key variable in both heat transfer and pressure drop correlations of two-phase flows, from the macro to micro- channel scale. Void fraction estimation dictates the sizing of both evaporating and condensing phase change heat exchangers, for example. In order to measure void fraction some invasive approach is necessary. Typically, visualization is achieved either downstream of the test section or on top by machining to expose the channel. Both approaches can lead to inaccuracies. The former assumes the flow will not be affected moving from the heat exchanger surface to the transparent section. The latter distorts the heat flow path. Neutron Imaging can provide a non-invasive measurement because metals such as Aluminum are essentially transparent to neutrons. Hence, if a refrigerant is selected that provides suitable neutron attenuation; steady-state void fraction measurements in two-phase flow are attainable in-situ without disturbing the fluid flow or heat flow path. Neutron Imaging has been used in the past to qualitatively describe the flow in heat exchangers in terms of maldistributions without providing void fraction data. This work is distinguished from previous efforts because the heat exchanger has been designed and the refrigerant selected to avail of neutron imaging. This work describes the experimental flow loop that enables a boiling two-phase flow; the heat exchanger test section and downstream transparent section are described. The flow loop controls the degree of subcooling and the refrigerant flowrate. Heating cartridges embedded in the test section are employed to control the heat input. Neutron-imaged steady-state void fraction measurements are captured and compared to representative high-speed videography captured at the visualization section. This allows a qualitative comparison between neutron imaged and traditional techniques. The
A real two-phase submarine debris flow and tsunami
Pudasaini, Shiva P.; Miller, Stephen A.
2012-09-26
The general two-phase debris flow model proposed by Pudasaini is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
Shanthi, C; Pappa, N
2017-02-13
Flow pattern recognition is necessary to select design equations for finding operating details of the process and to perform computational simulations. Visual image processing can be used to automate the interpretation of patterns in two-phase flow. In this paper, an attempt has been made to improve the classification accuracy of the flow pattern of gas/ liquid two- phase flow using fuzzy logic and Support Vector Machine (SVM) with Principal Component Analysis (PCA). The videos of six different types of flow patterns namely, annular flow, bubble flow, churn flow, plug flow, slug flow and stratified flow are recorded for a period and converted to 2D images for processing. The textural and shape features extracted using image processing are applied as inputs to various classification schemes namely fuzzy logic, SVM and SVM with PCA in order to identify the type of flow pattern. The results obtained are compared and it is observed that SVM with features reduced using PCA gives the better classification accuracy and computationally less intensive than other two existing schemes. This study results cover industrial application needs including oil and gas and any other gas-liquid two-phase flows.
BAYESIAN SEMIPARAMETRIC ANALYSIS FOR TWO-PHASE STUDIES OF GENE-ENVIRONMENT INTERACTION
Ahn, Jaeil; Mukherjee, Bhramar; Gruber, Stephen B.; Ghosh, Malay
2013-01-01
The two-phase sampling design is a cost-efficient way of collecting expensive covariate information on a judiciously selected sub-sample. It is natural to apply such a strategy for collecting genetic data in a sub-sample enriched for exposure to environmental factors for gene-environment interaction (G × E) analysis. In this paper, we consider two-phase studies of G × E interaction where phase I data are available on exposure, covariates and disease status. Stratified sampling is done to prioritize individuals for genotyping at phase II conditional on disease and exposure. We consider a Bayesian analysis based on the joint retrospective likelihood of phase I and phase II data. We address several important statistical issues: (i) we consider a model with multiple genes, environmental factors and their pairwise interactions. We employ a Bayesian variable selection algorithm to reduce the dimensionality of this potentially high-dimensional model; (ii) we use the assumption of gene-gene and gene-environment independence to trade-off between bias and efficiency for estimating the interaction parameters through use of hierarchical priors reflecting this assumption; (iii) we posit a flexible model for the joint distribution of the phase I categorical variables using the non-parametric Bayes construction of Dunson and Xing (2009). We carry out a small-scale simulation study to compare the proposed Bayesian method with weighted likelihood and pseudo likelihood methods that are standard choices for analyzing two-phase data. The motivating example originates from an ongoing case-control study of colorectal cancer, where the goal is to explore the interaction between the use of statins (a drug used for lowering lipid levels) and 294 genetic markers in the lipid metabolism/cholesterol synthesis pathway. The sub-sample of cases and controls on which these genetic markers were measured is enriched in terms of statin users. The example and simulation results illustrate that the
Two-phase electrochemical lithiation in amorphous silicon.
Wang, Jiang Wei; He, Yu; Fan, Feifei; Liu, Xiao Hua; Xia, Shuman; Liu, Yang; Harris, C Thomas; Li, Hong; Huang, Jian Yu; Mao, Scott X; Zhu, Ting
2013-02-13
Lithium-ion batteries have revolutionized portable electronics and will be a key to electrifying transport vehicles and delivering renewable electricity. Amorphous silicon (a-Si) is being intensively studied as a high-capacity anode material for next-generation lithium-ion batteries. Its lithiation has been widely thought to occur through a single-phase mechanism with gentle Li profiles, thus offering a significant potential for mitigating pulverization and capacity fade. Here, we discover a surprising two-phase process of electrochemical lithiation in a-Si by using in situ transmission electron microscopy. The lithiation occurs by the movement of a sharp phase boundary between the a-Si reactant and an amorphous Li(x)Si (a-Li(x)Si, x ~ 2.5) product. Such a striking amorphous-amorphous interface exists until the remaining a-Si is consumed. Then a second step of lithiation sets in without a visible interface, resulting in the final product of a-Li(x)Si (x ~ 3.75). We show that the two-phase lithiation can be the fundamental mechanism underpinning the anomalous morphological change of microfabricated a-Si electrodes, i.e., from a disk shape to a dome shape. Our results represent a significant step toward the understanding of the electrochemically driven reaction and degradation in amorphous materials, which is critical to the development of microstructurally stable electrodes for high-performance lithium-ion batteries.
Ultrasonic wave propagation in two-phase media: Spherical inclusions
NASA Technical Reports Server (NTRS)
Fu, L. S.; Sheu, Y. C.
1983-01-01
The scattering theory, recently developed via the extended method of equivalent inclusion, is used to study the propagation of time-harmonic waves in two-phase media of elastic matrix with randomly distributed elastic spherical inclusion materials. The elastic moduli and mass density of the composite medium are determined as functions of frequencies when given properties and concentration of the spheres and the matrix. Velocity and attenuation of ultrasonic waves in two-phase media are determined for cases of distributed spheres and localized damage. An averaging theorem that requires the equivalence of the strain energy and the kinetic energy between the effective medium and the original matrix with spherical inhomogeneities is employed to derive the effective moduli and mass density. The functional dependency of these quantities upon frequencies and concentration provides a method of data analysis in ultrasonic evaluation of material properties. Numerical results or moduli, velocity and/or attenuation as functions of concentration of inclusion material, or porosity, are graphically displayed.
Investigation of single-substance horizontal two-phase flow
Dickinson, D.A.; Maeder, P.F.
1984-03-01
Despite the abundance of work in the field of two-phase flow, it seems as though a consensus has not been reached on some of the fundamental points. Although exceptions exist, adequate physical interpretation of the flow seems to be hindered either by complexity of analysis or, in the opposite extreme, the trend toward limited-range analysis and correlations. The dissertation presents the derivation of basic conservation equations for the phases. The combined equations are used to examine the phenomenon of slip and its practical limitations, the Fanno line for single-substance flow and the effect of slip on choking. Equations for critical mass flux in the presence of slip are derived. The Mach, Reynolds and Froude numbers based on conditions at flashing are introduced as the characteristic parameters, and the importance of compressibility in single-substance two-phase flow is discussed. Experimental measurements of pressure change and void fraction for flow in the highly compressible range (.5 < Ma < 1) are presented. The working fluid is Refrigerant R-114, at room temperature, in a test section of diameter 5 cm and length 8 m. The effect of the Froude and Mach numbers is examined. The experimental facility is operated intermittently with running times of approximately two minutes and is instrumented for rapid measurements using a computer data acquisition and control system. A description of the facility and procedure is provided.
Nondestructive ultrasonic characterization of two-phase materials
NASA Technical Reports Server (NTRS)
Salama, Kamel
1987-01-01
The development of ultrasonic methods for the nondestructive characterization of mechanical properties of two phase engineering materials are described. The primary goal was to establish relationships between the nonlinearity parameter and the percentage of solid solution phase in two phase systems such as heat treatable aluminum alloys. The acoustoelastic constant was also measured on these alloys. A major advantage of the nonlinearity parameter over that of the acoustoelastic constant is that it may be determined without the application of stress on the material, which makes the method more applicable to inservice nondestructive characterization. The results obtained on the heat treatable 7075 and the work hardenable 5086 and 5456 aluminum alloys show that both the acoustoelastic constant and the acoustic nonlinearity parameter change considerable with the volume fraction of second phase precipitates in these aluminum alloys. A mathematical model was also developed to relate the effective acoustic nonlinearity parameter to volume fraction of second phase precipitates in an alloy. The equation is approximated to within experimental error by a linear expression for volume fractions up to approx. 10%.
Advanced two-phase digestion of sewage sludge
Ghosh, S.
1984-01-01
This paper describes the development and operating results of a novel configuration of the two-phase digestion concept. The two-phase system, comprises two custom-designed upflow digesters, which were operated in tandem to optimize the liquefying-acidification and acetogenesis-methanation reactions. The results are based on system operation for more than one year with a high-metal-content sewage sludge. During the operating period, the system exhibited an increasing methane yield at hydraulic retention times (HRT) of less than 6 days. With continuing culture enrichment and improvements in reactor design, the methane yield increased from 5 to 6.8 SCF/lb VS added, and then to 7.7 SCF/lb VS added. This methane yield was about 80% of the theoretical methane yield achievable with this sewage sludge--and the highest methane yield reported for sludge at this HRT. Operation of the novel process configuration was very stable and superior to that of conventional single-stage digestion in terms of methane yield, gas generation rate, and net energy production. About 75 weight percent of the organic solids was gasified; this could be the maximum attainable feed conversion efficiency for sludge, considering that between 75% and 80% of this feed is normally biodegradable. 3 references, 7 tables.
Aqueous Two Phase System Assisted Self-Assembled PLGA Microparticles
NASA Astrophysics Data System (ADS)
Yeredla, Nitish; Kojima, Taisuke; Yang, Yi; Takayama, Shuichi; Kanapathipillai, Mathumai
2016-06-01
Here, we produce poly(lactide-co-glycolide) (PLGA) based microparticles with varying morphologies, and temperature responsive properties utilizing a Pluronic F127/dextran aqueous two-phase system (ATPS) assisted self-assembly. The PLGA polymer, when emulsified in Pluronic F127/dextran ATPS, forms unique microparticle structures due to ATPS guided-self assembly. Depending on the PLGA concentration, the particles either formed a core-shell or a composite microparticle structure. The microparticles facilitate the simultaneous incorporation of both hydrophobic and hydrophilic molecules, due to their amphiphilic macromolecule composition. Further, due to the lower critical solution temperature (LCST) properties of Pluronic F127, the particles exhibit temperature responsiveness. The ATPS based microparticle formation demonstrated in this study, serves as a novel platform for PLGA/polymer based tunable micro/nano particle and polymersome development. The unique properties may be useful in applications such as theranostics, synthesis of complex structure particles, bioreaction/mineralization at the two-phase interface, and bioseparations.
Two-phase deformation of lower mantle mineral analogs
NASA Astrophysics Data System (ADS)
Kaercher, P.; Miyagi, L.; Kanitpanyacharoen, W.; Zepeda-Alarcon, E.; Wang, Y.; Parkinson, D.; Lebensohn, R. A.; De Carlo, F.; Wenk, H. R.
2016-12-01
The lower mantle is estimated to be composed of mostly bridgmanite and a smaller percentage of ferropericlase, yet very little information exists for two-phase deformation of these minerals. To better understand the rheology and active deformation mechanisms of these lower mantle minerals, especially dislocation slip and the development of crystallographic preferred orientation (CPO), we deformed mineral analogs neighborite (NaMgF3, iso-structural with bridgmanite) and halite (NaCl, iso-structural with ferropericlase) together in the deformation-DIA at the Advanced Photon Source up to 51% axial shortening. Development of CPO was recorded in situ with X-ray diffraction, and information on microstructural evolution was collected using X-ray microtomography. Results show that when present in as little as 15% volume, the weak phase (NaCl) controls the deformation. Compared to single phase NaMgF3 samples, samples with just 15% volume NaCl show a reduction of CPO in NaMgF3 and weakening of the aggregate. Microtomography shows both NaMgF3 and NaCl form highly interconnected networks of grains. Polycrystal plasticity simulations were carried out to gain insight into slip activity, CPO evolution, and strain and stress partitioning between phases for different synthetic two-phase microstructures. The results suggest that ferropericlase may control deformation in the lower mantle and reduce CPO in bridgmanite, which implies a less viscous lower mantle and helps to explain why the lower mantle is fairly isotropic.
Diffusion analysis for two-phase metal-matrix composite
NASA Technical Reports Server (NTRS)
Tenney, D. R.
1976-01-01
Diffusion controlled filament matrix interaction in a metal matrix composite, where the filaments and matrix comprise a two phase binary alloy system, was mathematically modeled. The problem of a diffusion controlled, two phase moving interface by means of a one dimensional, variable grid, finite difference technique was analyzed. Concentration dependent diffusion coefficients and equilibrium solubility limits were used, and the change in filament diameter and compositional changes in the matrix were calculated as a function of exposure time at elevated temperatures. With the tungsten nickel (W-Ni) system as a model composite system, unidirectional composites containing from 0.06 to 0.44 initial filament volume fraction were modeled. Compositional changes in the matrix were calculated by superposition of the contributions from neighboring filaments. Alternate methods for determining compositional changes between first and second nearest neighbor filaments were also considered. The results show the relative importance of filament volume fraction, filament diameter, exposure temperature, and exposure time as they affect the rate and extent of filament matrix interaction.
Droplets formation and merging in two-phase flow microfluidics.
Gu, Hao; Duits, Michel H G; Mugele, Frieder
2011-01-01
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
Droplets Formation and Merging in Two-Phase Flow Microfluidics
Gu, Hao; Duits, Michel H. G.; Mugele, Frieder
2011-01-01
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed. PMID:21731459
Smart microgels for controlling two-phase fluid structure in porous media
NASA Astrophysics Data System (ADS)
Fan, Jing; Weitz, David
Understanding the transport of microgels in porous media directly benefits the conformance improvement technique using preformed gels in the oil industry. We develop a new type of microgels that can swell in response to specific stimuli in an aqueous environment. From a practical point of view, this enables us to deliver the microgels to the deep reservoir formation and control the permeability profile more effectively. With confocal microscopy imaging, we show that we can deliver such smart microgels to the high-permeability region in a stratified porous medium, which subsequently changes the two-phase fluid structure in the medium. From a scientific point of view, this allows for characterizing the permeability change due to homogeneous pore-clogging by soft particles instead of surface clogging; using the typical microgels this can hardly be done because we cannot place gel particles with comparable size to the pore uniformly into a porous medium. This study may shed light on understanding many other processes involving the transport of soft particles in porous structures. The authors acknowledge the financial support from Advanced Energy Consortium, BEG08-27.
Numerical Simulation of Two-phase flow with Phase Change Using the Level-set Method
NASA Astrophysics Data System (ADS)
Li, Hongying; Lou, Jing; Pan, Lunsheng; Yap, Yitfatt
2016-11-01
Multiphase flow with phase change is widely encountered in many engineering applications. A distinct feature involves in these applications is the phase transition from one phase to another due to the non-uniform temperature distribution. Such kind of process generally releases or absorbs large amount of energy with mass transfer happened simultaneously. It demands great cautions occasionally such as the high pressure due to evaporation. This article presents a numerical model for simulation of two-fluid flow with phase change problem. In these two fluids, one of them changes its state due to phase change. Such a problem then involves two substances with three phases as well as two different interfaces, i.e. the interface between two substances and the interface of one substance between its two phases. Two level-set functions are used to capture the two interfaces in the current problem. The current model is validated against one-dimensional and two-dimensional liquid evaporation. With the code validated, it is applied to different phase change problems including (1) a falling evaporating droplet and the rising of one bubble and (2) two-fluid stratified flow with solidification of one fluid. Comparisons on the bubble and droplet topologies, flow and temperature fields are made for the first case between the falling evaporating droplet and the falling droplet without evaporation. For the second demonstration case, the effect of the superheated temperature on the solidification process is investigated.
Gas-liquid two phase flow through a vertical 90 elbow bend
Spedding, P.L.; Benard, E.
2007-07-15
Pressure drop data are reported for two phase air-water flow through a vertical to horizontal 90 elbow bend set in 0.026 m i.d. pipe. The pressure drop in the vertical inlet tangent showed some significant differences to that found for straight vertical pipe. This was caused by the elbow bend partially choking the inflow resulting in a build-up of pressure and liquid in the vertical inlet riser and differences in the structure of the flow regimes when compared to the straight vertical pipe. The horizontal outlet tangent by contrast gave data in general agreement with literature even to exhibiting a drag reduction region at low liquid rates and gas velocities between 1 and 2 m s{sup -1}. The elbow bend pressure drop was best correlated in terms of l{sub e}/d determined using the actual pressure loss in the inlet vertical riser. The data showed a general increase with fluid rates that tapered off at high fluid rates and exhibited a negative pressure region at low rates. The latter was attributed to the flow being smoothly accommodated by the bend when it passed from slug flow in the riser to smooth stratified flow in the outlet tangent. A general correlation was presented for the elbow bend pressure drop in terms of total Reynolds numbers. A modified Lockhart-Martinelli model gave prediction of the data. (author)
The development of two-phase xenon dark matter detectors
NASA Astrophysics Data System (ADS)
Kwong, John
The nature of dark matter remains one of the great unsolved mysteries of modern physics. The existence of dark matter has been inferred from its gravitational interactions and is strongly supported on theoretical grounds. A primary candidate for the dark matter is the Weakly Interacting Massive Particle (WIMP), which may be an undiscovered particle from the supersymmetric sector. This dissertation describes the research and development in two-phase liquid xenon dark matter detector technology and the results from the full-scale detector XENON10. Two-phase liquid xenon detectors use position sensitivity and simultaneous measurement of light and charge to remove background electron recoil events. The development of this technology has been rapid - the work in this dissertation began in the summer of 2003 when the potential of this technology had yet to be determined, and in early 2008 the XENON10 collaboration published the then world-best upper limit on the spin-independent WIMP-nucleon cross section. The first measurement of the charge based discrimination performance at low energies was achieved in a prototype in early 2005. This prototype also determined the performance of discrimination via scintillation pulse shape. Although pulse shape discrimination was shown to be far weaker than that from charge yield, the combined use of the two methods demonstrated a discrimination power beyond that achieved by either method alone. Alternative detector technologies were also explored. Electron multiplication on wire grids was demonstrated in a two-phase prototype and its discrimination power potential is shown to be near that of the typical electroluminescence charge-readout technique. This could allow for the removal of some or all of the photo-multipliers in the detector, which would greately reduce radioactive backgrounds. The use of a wavelength shifter was tested in an attempt to improve light collection and was shown to impede charge collection. The magnitude of
Two-phase microfluidics: thermophysical fundamentals and engineering concepts
NASA Astrophysics Data System (ADS)
Kuznetsov, V. V.
2016-10-01
Thermophysical fundamentals and engineering concepts of the two-phase microfluidic devises based on controlled liquid decay are discussed in this paper. The results of an experimental study of the explosive evaporation at a thin film heater of the MEMS devise in application to thermal inkjet printing are presented. The peculiarities of homogeneous nucleation and bubble growth in the liquid subjected to pulse heating are discussed. Using experimental data a simple equation suitable for predicting the growth rate of a vapor bubble in a non-uniformly superheated liquid was obtained and used to complete a mathematical model of the self-consistent nucleation and vapor bubbles growth in the induced pressure field. The results of numerical calculations according to the proposed model showed good agreement with the experimental data on a time of nucleation and duration of the initial stage of an explosive evaporation of water.
Theory and tests of two-phase turbines
NASA Technical Reports Server (NTRS)
Elliott, D. G.
1982-01-01
A theoretical model for two-phase turbines was developed. Apparatus was constructed for testing one- and two-stage turbines (using speed decrease from stage to stage). Turbines were tested with water and nitrogen mixtures and refrigerant 22. Nozzle efficiencies were 0.78 (measured) and 0.72 (theoretical) for water and nitrogen mixtures at a water/nitrogen mixture ratio of 68, by mass; and 0.89 (measured) and 0.84 (theoretical) for refrigerant 22 expanding from 0.02 quality to 0.28 quality. Blade efficiencies (shaft power before windage and bearing loss divided by nozzle jet power) were 0.63 (measured) and 0.71 (theoretical) for water and nitrogen mixtures and 0.62 (measured) and 0.63 (theoretical) for refrigerant 22 with a single stage turbine, and 0,70 (measured) and 0.85 (theoretical) for water and nitrogen mixtures with a two-stage turbine.
Tsunami Generated by a Two-Phase Submarine Debris Flow
NASA Astrophysics Data System (ADS)
Pudasaini, S. P.
2012-04-01
The general two-phase debris flow model proposed by Pudasaini (2011) is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model includes several essential physical aspects, including Mohr-Coulomb plasticity for the solid stress, while the fluid stress is modelled as a solid volume fraction gradient enhanced non-Newtonian viscous stress. The generalized interfacial momentum transfer includes the viscous drag, buoyancy, and the virtual mass. The generalized drag covers both the solid-like and fluid-like contributions, and can be applied to linear to quadratic drags. Strong couplings exist between the solid and the fluid momentum transfer. The advantage of the real two-phase debris flow model over classical single-phase or quasi-two-phase models is that by considering the solid (and/or the fluid) volume fraction appropriately, the initial mass can be divided into several (even mutually disjoint) parts; a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This offers a unique and innovative opportunity within a single framework to simultaneously simulate (a) the sliding debris (or landslide), (b) the water lake or ocean, (c) the debris impact at the lake or ocean, (d) tsunami generation and propagation, (e) mixing and separation between the solid and the fluid phases, and (f) sediment transport and deposition process in the bathymetric surface. The new model is applied to two-phase subaerial and submarine debris flows. Benchmark numerical simulations reveal that the dynamics of the debris impact induced tsunamis are fundamentally different than the tsunami generated by pure rock avalanche and landslides. Special attention is paid to study the basic features of the debris impact to the mountain lakes or oceans. This includes the generation, amplification and propagation of the multiple
Conservation laws for two-phase filtration models
NASA Astrophysics Data System (ADS)
Baikov, V. A.; Ibragimov, N. H.; Zheltova, I. S.; Yakovlev, A. A.
2014-02-01
The paper is devoted to investigation of group properties of a one-dimensional model of two-phase filtration in porous medium. Along with the general model, some of its particular cases widely used in oil-field development are discussed. The Buckley-Leverett model is considered in detail as a particular case of the one-dimensional filtration model. This model is constructed under the assumption that filtration is one-dimensional and horizontally directed, the porous medium is homogeneous and incompressible, the filtering fluids are also incompressible. The model of "chromatic fluid" filtration is also investigated. New conservation laws and particular solutions are constructed using symmetries and nonlinear self-adjointness of the system of equations.
Design of an advanced two-phase capillary cold plate
NASA Technical Reports Server (NTRS)
Chalmers, D. R.; Kroliczek, E. J.; Ku, J.
1986-01-01
The functional principles and implementation of capillary pumped loop (CPL) two phase heat transport system for various elements of the Space Station program are described. Circulation of the working fluid by the surface-tension forces in a fine-pore capillary wick is the core principle of CPL systems. The liquid, usually NH3 at the moment, is changed into a vapor by heat absorption at one end of the loop, and the vapor is carrried back along the wick by the surface tension within the wick. NASA specifications and the results of mechanical and thermal tests for prototype cold plate and the capillary pump designs are outlined. The CPL is targeted for installation on free-flying platforms, attached payloads, and power subsystem thermal control systems.
Emerging Two-Phase Cooling Technologies for Power Electronic Inverters
Hsu, J.S.
2005-08-17
In order to meet the Department of Energy's (DOE's) FreedomCAR and Vehicle Technologies (FVCT) goals for volume, weight, efficiency, reliability, and cost, the cooling of the power electronic devices, traction motors, and generators is critical. Currently the power electronic devices, traction motors, and generators in a hybrid electric vehicle (HEV) are primarily cooled by water-ethylene glycol (WEG) mixture. The cooling fluid operates as a single-phase coolant as the liquid phase of the WEG does not change to its vapor phase during the cooling process. In these single-phase systems, two cooling loops of WEG produce a low temperature (around 70 C) cooling loop for the power electronics and motor/generator, and higher temperature loop (around 105 C) for the internal combustion engine. There is another coolant option currently available in automobiles. It is possible to use the transmission oil as a coolant. The oil temperature exists at approximately 85 C which can be utilized to cool the power electronic and electrical devices. Because heat flux is proportional to the temperature difference between the device's hot surface and the coolant, a device that can tolerate higher temperatures enables the device to be smaller while dissipating the same amount of heat. Presently, new silicon carbide (SiC) devices and high temperature direct current (dc)-link capacitors, such as Teflon capacitors, are available but at significantly higher costs. Higher junction temperature (175 C) silicon (Si) dies are gradually emerging in the market, which will eventually help to lower hardware costs for cooling. The development of high-temperature devices is not the only way to reduce device size. Two-phase cooling that utilizes the vaporization of the liquid to dissipate heat is expected to be a very effective cooling method. Among two-phase cooling methods, different technologies such as spray, jet impingement, pool boiling and submersion, etc. are being developed. The Oak Ridge
Flooding in counter-current two-phase flow
Ragland, W.A.; Ganic, E.N.
1982-01-01
Flooding is a phenomenon which is best described as the transition from counter-current to co-current flow. Early notice was taken of this phenomenon in the chemical engineering industry. Flooding also plays an important role in the field of two-phase heat transfer since it is a limit for many systems involving counter-current flow. Practical applications of flooding limited processes include wickless thermosyphons and the emergency core cooling system (ECCS) of pressurized water nuclear reactors. The phenomenon of flooding also is involved in the behavior of nuclear reactor core materials during severe accident conditions where flooding is one of the mechanisms governing the motion of the molten fuel pin cladding.
Vapor core turbulence in annular two-phase flow
Trabold, T.A.; Kumar, R.
1998-06-01
This paper reports a new technique to measure vapor turbulence in two-phase flows using hot-film anemometry. Continuous vapor turbulence measurements along with local void fraction, droplet frequency, droplet velocity and droplet diameter were measured in a thin, vertical duct. By first eliminating the portion of the output voltage signal resulting from the interaction of dispersed liquid droplets with the HFA sensor, the discrete voltage samples associated with the vapor phase were separately analyzed. The data revealed that, over the range of liquid droplet sizes and concentrations encountered, the presence of the droplet field acts to enhance vapor turbulence. In addition, there is evidence that vapor turbulence is significantly influenced by the wall-bounded liquid film. The present results are qualitatively consistent with the limited data available in the open literature.
Measurement of two-phase flow momentum with force transducers
Hardy, J.E.; Smith, J.E.
1990-01-01
Two strain-gage-based drag transducers were developed to measure two-phase flow in simulated pressurized water reactor (PWR) test facilities. One transducer, a drag body (DB), was designed to measure the bidirectional average momentum flux passing through an end box. The second drag sensor, a break through detector (BTD), was designed to sense liquid downflow from the upper plenum to the core region. After prototype sensors passed numerous acceptance tests, transducers were fabricated and installed in two experimental test facilities, one in Japan and one in West Germany. High-quality data were extracted from both the DBs and BTDs for a variety of loss-of-coolant accident (LOCA) scenarios. The information collected from these sensors has added to the understanding of the thermohydraulic phenomena that occur during the refill/reflood stage of a LOCA in a PWR. 9 refs., 15 figs.
Two-phase flow cell for chemiluminescence and bioluminescence measurements
Mullin, J.L.; Seitz, W.R.
1984-01-01
A new approach to two-phase CL (chemiluminescence) measurements is reported. A magnetically stirred reagent phase is separated from the analyte phase by a dialysis membrane so that only smaller molecules can go from one phase to the other. The system is designed so that the analyte phase flows through a spiral groove on an aluminum block that is flush against the dialysis membrane. As solution flows through the spiral grove, analyte diffuses into the reagent phase where it reacts to produce light. A simple model is developed to predict how this system will behave. Experimentally, the system is evaluated by using the luminol reaction catalyzed by peroxidase, the firefly reaction, and the bacterial bioluminescence reaction. 10 references, 4 tables, 6 figures.
Transient thermohydraulic modeling of two-phase fluid systems
NASA Astrophysics Data System (ADS)
Blet, N.; Delalandre, N.; Ayel, V.; Bertin, Y.; Romestant, C.; Platel, V.
2012-11-01
This paper presents a transient thermohydraulic modeling, initially developed for a capillary pumped loop in gravitational applications, but also possibly suitable for all kinds of two-phase fluid systems. Using finite volumes method, it is based on Navier-Stokes equations for transcribing fluid mechanical aspects. The main feature of this 1D-model is based on a network representation by analogy with electrical. This paper also proposes a parametric study of a counterflow condenser following the sensitivity to inlet mass flow rate and cold source temperature. The comparison between modeling results and experimental data highlights a good numerical evaluation of temperatures. Furthermore, the model is able to represent a pretty good dynamic evolution of hydraulic variables.
Rationale for two phase polymer system microgravity separation experiments
NASA Technical Reports Server (NTRS)
Brooks, D. E.; Bamberger, S. B.; Harris, J. M.; Vanalstine, J.
1984-01-01
The two-phase systems that result when aqueous solutions of dextran and poly(ethylene glycol) are mixed at concentrations above a few percent are discussed. They provide useful media for the partition and isolation of macromolecules and cell subpopulations. By manipulating their composition, separations based on a variety of molecular and surface properties are achieved, including membrane hydrophobic properties, cell surface charge, and membrane antigenicity. Work on the mechanism of cell partition shows there is a randomizing, nonthermal energy present which reduces separation resolution. This stochastic energy is probably associated with hydrodynamic interactions present during separation. Because such factors should be markedly reduced in microgravity, a series of shuttle experiments to indicate approaches to increasing the resolution of the procedure are planned.
Interfacial shear modeling in two-phase annular flow
Kumar, R.; Edwards, D.P.
1996-11-01
A new interfacial shear stress model called the law of the interface model, based on the law of the wall approach in turbulent flows, has been developed and locally applied in a fully developed, adiabatic, two-phase annular flow in a duct. Numerical results have been obtained using this model in conjunction with other models available in the literature that are required for the closure of the continuity and momentum equations. These results have been compared with droplet velocity data (using laser Doppler velocimetry and hot film anemometry), void fraction data (using gamma densitometry) and pressure drop data obtained in a R-134A refrigerant test facility. Droplet velocity results match the experimental data well, however, the prediction of the void fraction is less accurate. The poor prediction of void fraction, especially for the low void fraction cases, appears to be due to the lack of a good mechanistic model for entrainment.
Interfacial shear modeling in two-phase annular flow
Kumar, R.; Edwards, D.P.
1996-07-01
A new interfacial shear stress model called the law of the interface model, based on the law of the wall approach in turbulent flows, has been developed and locally applied in a fully developed, adiabatic, two-phase annular flow in a duct. Numerical results have been obtained using this model in conjunction with other models available in the literature that are required for the closure of the continuity and momentum equations. These results have been compared with droplet velocity data (using laser Doppler velocimetry and hot film anemometry), void fraction data (using gamma densitometry) and pressure drop data obtained in a R-134A refrigerant test facility. Droplet velocity results match the experimental data well, however, the prediction of the void fraction is less accurate. The poor prediction of void fraction, especially for the low void fraction cases, appears to be due to the lack of a good mechanistic model for entrainment.
Response of two-phase droplets to intense electromagnetic radiation
NASA Technical Reports Server (NTRS)
Spann, James F.; Maloney, Daniel J.; Lawson, William F.; Casleton, Kent H.
1993-01-01
The response of two-phase droplets to intense radiant heating is studied to determine the incident power that is required for causing explosive boiling in the liquid phase. The droplets studied consist of strongly absorbing coal particles dispersed in a weakly absorbing water medium. Experiments are performed by confining droplets (radii of 37, 55, and 80 microns) electrodynamically and irradiating them from two sides with pulsed laser beams. Emphasis is placed on the transition region from accelerated droplet vaporization to droplet superheating and explosive boiling. The time scale observed for explosive boiling is more than 2 orders of magnitude longer than published values for pure liquids. The delayed response is the result of energy transfer limitations between the absorbing solid phase and the surrounding liquid.
Higher order time integration methods for two-phase flow
NASA Astrophysics Data System (ADS)
Kees, Christopher E.; Miller, Cass T.
Time integration methods that adapt in both the order of approximation and time step have been shown to provide efficient solutions to Richards' equation. In this work, we extend the same method of lines approach to solve a set of two-phase flow formulations and address some mass conservation issues from the previous work. We analyze these formulations and the nonlinear systems that result from applying the integration methods, placing particular emphasis on their index, range of applicability, and mass conservation characteristics. We conduct numerical experiments to study the behavior of the numerical models for three test problems. We demonstrate that higher order integration in time is more efficient than standard low-order methods for a variety of practical grids and integration tolerances, that the adaptive scheme successfully varies the step size in response to changing conditions, and that mass balance can be maintained efficiently using variable-order integration and an appropriately chosen numerical model formulation.
Particle-fluid two-phase flow modeling
Mortensen, G.A.; Trapp, J.A. |
1992-09-01
This paper describes a numerical scheme and computer program, DISCON, for the calculation of two-phase flows that does not require the use of flow regime maps. This model is intermediate between-thermal instantaneous and the averaged two-fluid model. It solves the Eulerian continuity, momentum, and energy equations for each liquid control volume, and the Lagrangian mass, momentum, energy, and position equations for each bubble. The bubbles are modeled individually using a large representative number of bubbles thus avoiding the numerical diffusion associated with Eulerian models. DISCON has been used to calculate the bubbling of air through a column of water and the subcooled boiling of water in a flow channel. The results of these calculations are presented.
Particle-fluid two-phase flow modeling
Mortensen, G.A. ); Trapp, J.A. Idaho National Engineering Lab., Idaho Falls, ID )
1992-01-01
This paper describes a numerical scheme and computer program, DISCON, for the calculation of two-phase flows that does not require the use of flow regime maps. This model is intermediate between-thermal instantaneous and the averaged two-fluid model. It solves the Eulerian continuity, momentum, and energy equations for each liquid control volume, and the Lagrangian mass, momentum, energy, and position equations for each bubble. The bubbles are modeled individually using a large representative number of bubbles thus avoiding the numerical diffusion associated with Eulerian models. DISCON has been used to calculate the bubbling of air through a column of water and the subcooled boiling of water in a flow channel. The results of these calculations are presented.
Two-phase flow instabilities in a vertical annular channel
Babelli, I.; Nair, S.; Ishii, M.
1995-09-01
An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.
Conceptual design for spacelab two-phase flow experiments
NASA Technical Reports Server (NTRS)
Bradshaw, R. D.; King, C. D.
1977-01-01
KC-135 aircraft tests confirmed the gravity sensitivity of two phase flow correlations. The prime component of the apparatus is a 1.5 cm dia by 90 cm fused quartz tube test section selected for visual observation. The water-cabin air system with water recycle was a clear choice for a flow regime-pressure drop test since it was used satisfactorily on KC-135 tests. Freon-11 with either overboard dump or with liquid-recycle will be used for the heat transfer test. The two experiments use common hardware. The experimental plan covers 120 data points in six hours with mass velocities from 10 to 640 kg/sec-sq m and qualities 0.01 to 0.64. The apparatus with pump, separator, storage tank and controls is mounted in a double spacelab rack. Supporting hardware, procedures, measured variables and program costs are defined.
Two-phase partitioning bioreactors in environmental biotechnology.
Quijano, Guillermo; Hernandez, María; Thalasso, Frédéric; Muñoz, Raúl; Villaverde, Santiago
2009-10-01
Two-phase partitioning bioreactors (TPPBs) in environmental biotechnology are based on the addition of a non-aqueous phase (NAP) into a biological process in order to overcome both mass-transfer limitations from the gas to aqueous phase and pollutant-mediated inhibitions. Despite constituting a robust and reliable technology in terms of pollutant biodegradation rates and process stability in wastewater, soil, and gas treatment applications, this superior performance only applies for a restricted number of pollutants or contamination events. Severe limitations such as high energy requirements, high costs of some NAPs, foaming, or pollutant sequestration challenge the full-scale application of this technology. The introduction of solid NAPs into this research field has opened a promising pathway for the future development of TPPBs. Finally, this work reviews fundamental aspects of NAP selection and mass transfer and identifies the niches for future research: low energy-demand bioreactor designs, experimental determination of partial mass transfers, and solid NAP tailoring.
Stratified volume diffractive optical elements
NASA Astrophysics Data System (ADS)
Chambers, Diana Marie
2000-11-01
Gratings with high diffraction efficiency into a single order find use in applications ranging from optical interconnects to beam steering. Such gratings have been realized with volume holographic, blazed, and diffractive optical techniques. However, each of these methods has limitations that restrict the range of applications in which they can be used. In this work an alternate, novel approach and method for creating high efficiency gratings has been developed. These new gratings are named stratified volume diffractive optical elements (SVDOE's). In this approach diffractive optic techniques are used to create an optical structure that emulates volume grating behavior. An SVDOE consists of binary gratings interleaved with homogeneous layers in a multi-layer, stratified grating structure. The ridges of the binary gratings form fringe planes analogous to those of a volume hologram. The modulation and diffraction of an incident beam, which occur concurrently in a volume grating, are achieved sequentially by the grating layers and the homogeneous layers, respectively. The layers in this type of structure must be fabricated individually, which introduces the capability to laterally shift the binary grating layers relative to one another to create a grating with slanted fringe planes. This allows an element to be designed with high diffraction efficiency into the first order for any arbitrary angle of incidence. A systematic design process has been developed for SVDOE's. Optimum modulation depth of the SVDOE is determined analytically and the number of grating layers along with the thickness of homogeneous layers is determined by numerical simulation. A rigorous electromagnetic simulation of the diffraction properties of multi-layer grating structures, based on the Rigorous Coupled-Wave Analysis (RCWA) algorithm, was developed and applied to SVDOE performance prediction. Fabrication of an SVDOE structure presents unique challenges. Microfabrication combined with
Supporting universal prevention programs: a two-phased coaching model.
Becker, Kimberly D; Darney, Dana; Domitrovich, Celene; Keperling, Jennifer Pitchford; Ialongo, Nicholas S
2013-06-01
Schools are adopting evidence-based programs designed to enhance students' emotional and behavioral competencies at increasing rates (Hemmeter et al. in Early Child Res Q 26:96-109, 2011). At the same time, teachers express the need for increased support surrounding implementation of these evidence-based programs (Carter and Van Norman in Early Child Educ 38:279-288, 2010). Ongoing professional development in the form of coaching may enhance teacher skills and implementation (Noell et al. in School Psychol Rev 34:87-106, 2005; Stormont et al. 2012). There exists a need for a coaching model that can be applied to a variety of teacher skill levels and one that guides coach decision-making about how best to support teachers. This article provides a detailed account of a two-phased coaching model with empirical support developed and tested with coaches and teachers in urban schools (Becker et al. 2013). In the initial universal coaching phase, all teachers receive the same coaching elements regardless of their skill level. Then, in the tailored coaching phase, coaching varies according to the strengths and needs of each teacher. Specifically, more intensive coaching strategies are used only with teachers who need additional coaching supports, whereas other teachers receive just enough support to consolidate and maintain their strong implementation. Examples of how coaches used the two-phased coaching model when working with teachers who were implementing two universal prevention programs (i.e., the PATHS curriculum and PAX Good Behavior Game [PAX GBG]) provide illustrations of the application of this model. The potential reach of this coaching model extends to other school-based programs as well as other settings in which coaches partner with interventionists to implement evidence-based programs.
Supporting Universal Prevention Programs: A Two-Phased Coaching Model
Becker, Kimberly D.; Darney, Dana; Domitrovich, Celene; Keperling, Jennifer Pitchford; Ialongo, Nicholas S.
2013-01-01
Schools are adopting evidence-based programs designed to enhance students’ emotional and behavioral competencies at increasing rates (Hemmeter, Snyder, & Artman, 2011). At the same time, teachers express the need for increased support surrounding implementation of these evidence-based programs (Carter & Van Norman, 2010). Ongoing professional development in the form of coaching may enhance teacher skills and implementation (Noell et al., 2005; Stormont, Reinke, Newcomer, Darney, & Lewis, 2012). There exists a need for a coaching model that can be applied to a variety of teacher skill levels and one that guides coach decision-making about how best to support teachers. This article provides a detailed account of a two-phased coaching model with empirical support developed and tested with coaches and teachers in urban schools (Becker, Bradshaw, Domitrovich, & Ialongo, 2013). In the initial universal coaching phase, all teachers receive the same coaching elements regardless of their skill level. Then, in the tailored coaching phase, coaching varies according to the strengths and needs of each teacher. Specifically, more intensive coaching strategies are used only with teachers who need additional coaching supports whereas other teachers receive just enough support to consolidate and maintain their strong implementation. Examples of how coaches used the two-phased coaching model when working with teachers who were implementing two universal prevention programs (i.e., the PATHS® curriculum and PAX Good Behavior Game [PAX GBG]) provide illustrations of the application of this model. The potential reach of this coaching model extends to other school-based programs as well as other settings in which coaches partner with interventionists to implement evidence-based programs. PMID:23660973
Correct numerical simulation of a two-phase coolant
NASA Astrophysics Data System (ADS)
Kroshilin, A. E.; Kroshilin, V. E.
2016-02-01
Different models used in calculating flows of a two-phase coolant are analyzed. A system of differential equations describing the flow is presented; the hyperbolicity and stability of stationary solutions of the system is studied. The correctness of the Cauchy problem is considered. The models' ability to describe the following flows is analyzed: stable bubble and gas-droplet flows; stable flow with a level such that the bubble and gas-droplet flows are observed under and above it, respectively; and propagation of a perturbation of the phase concentration for the bubble and gas-droplet media. The solution of the problem about the breakdown of an arbitrary discontinuity has been constructed. Characteristic times of the development of an instability at different parameters of the flow are presented. Conditions at which the instability does not make it possible to perform the calculation are determined. The Riemann invariants for the nonlinear problem under consideration have been constructed. Numerical calculations have been performed for different conditions. The influence of viscosity on the structure of the discontinuity front is studied. Advantages of divergent equations are demonstrated. It is proven that a model used in almost all known investigating thermohydraulic programs, both in Russia and abroad, has significant disadvantages; in particular, it can lead to unstable solutions, which makes it necessary to introduce smoothing mechanisms and a very small step for describing regimes with a level. This does not allow one to use efficient numerical schemes for calculating the flow of two-phase currents. A possible model free from the abovementioned disadvantages is proposed.
Interfacial characteristic measurements in horizontal bubbly two-phase flow
NASA Astrophysics Data System (ADS)
Wang, Z.; Huang, W. D.; Srinivasmurthy, S.; Kocamustafaogullari, G.
1990-10-01
Advances in the study of two-phase flow increasingly require detailed internal structure information upon which theoretical models can be formulated. The void fraction and interfacial area are two fundamental parameters characterizing the internal structure of two-phase flow. However, little information is currently available on these parameters, and it is mostly limited to vertical flow configurations. In view of the above, the internal phase distribution of concurrent, air-water bubbly flow in a 50.3 mm diameter transparent pipeline has been experimentally investigated by using a double-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 3.74 to 5.60 m/s and 0.25 to 1.59 m/s, respectively, and average void fractions ranged from 2.12 to 22.5 percent. The local values of void fractions, interfacial area concentration, mean bubble diameter, bubble interface velocity, bubble chord-length and bubble frequency distributions were measured. The experimental results indicate that the void fraction interfacial area concentration and bubble frequency have local maxima near the upper pipe wall, and the profiles tend to flatten with increasing void fraction. The observed peak void fraction can reach 0.65, the peak interfacial area can go up to 900 approximately 1000 sq m/cu m, and the bubble frequency can reach a value of 2200 per s. These ranges of values have never been reported for vertical bubbly flow. It is found that either decreasing the liquid flow rate or increasing the gas flow would increase the local void fraction, the interfacial area concentration and the bubble frequency.
Two-phase methanization of food wastes in pilot scale.
Lee, J P; Lee, J S; Park, S C
1999-01-01
A 5 ton/d pilot scale two-phase anaerobic digester was constructed and tested to treat Korean food wastes in Anyang city near Seoul. The easily degradable presorted food waste was efficiently treated in the two-phase anaerobic digestion process. The waste contained in plastic bags was shredded and then screened for the removal of inert materials such as fabrics and plastics, and subsequently put into the two-stage reactors. Heavy and light inerts such as bones, shells, spoons, and plastic pieces were again removed by gravity differences. The residual organic component was effectively hydrolyzed and acidified in the first reactor with 5 d space time at pH of about 6.5. The second, methanization reactor converted the acids into methane with pH between 7.4 and 7.8. The space time for the second reactor was 15 d. The effluent from the second reactor was recycled to the first reactor to provide alkalinities. The process showed stable steady-state operation with the maximum organic loading rate of 7.9 kg volatile solid (VS)/m3/d and the volatile solid reduction efficiency of about 70%. The total of 3.6 tons presorted MSW containing 2.9 tons of food organic was treated to produce about 230 m3 of biogas with 70% (v/v) of methane and 80 kg of humus. This process is extended to full-scale treating 15 tons of food waste a day in Euiwang city and the produced biogas is utilized for the heating/cooling of adjacent buildings.
A New Void Fraction Measurement Method for Gas-Liquid Two-Phase Flow in Small Channels
Li, Huajun; Ji, Haifeng; Huang, Zhiyao; Wang, Baoliang; Li, Haiqing; Wu, Guohua
2016-01-01
Based on a laser diode, a 12 × 6 photodiode array sensor, and machine learning techniques, a new void fraction measurement method for gas-liquid two-phase flow in small channels is proposed. To overcome the influence of flow pattern on the void fraction measurement, the flow pattern of the two-phase flow is firstly identified by Fisher Discriminant Analysis (FDA). Then, according to the identification result, a relevant void fraction measurement model which is developed by Support Vector Machine (SVM) is selected to implement the void fraction measurement. A void fraction measurement system for the two-phase flow is developed and experiments are carried out in four different small channels. Four typical flow patterns (including bubble flow, slug flow, stratified flow and annular flow) are investigated. The experimental results show that the development of the measurement system is successful. The proposed void fraction measurement method is effective and the void fraction measurement accuracy is satisfactory. Compared with the conventional laser measurement systems using standard laser sources, the developed measurement system has the advantages of low cost and simple structure. Compared with the conventional void fraction measurement methods, the proposed method overcomes the influence of flow pattern on the void fraction measurement. This work also provides a good example of using low-cost laser diode as a competent replacement of the expensive standard laser source and hence implementing the parameter measurement of gas-liquid two-phase flow. The research results can be a useful reference for other researchers’ works. PMID:26828488
PHOTOSPHERIC EMISSION FROM STRATIFIED JETS
Ito, Hirotaka; Nagataki, Shigehiro; Ono, Masaomi; Lee, Shiu-Hang; Mao, Jirong; Yamada, Shoichi; Pe'er, Asaf; Mizuta, Akira; Harikae, Seiji
2013-11-01
We explore photospheric emissions from stratified two-component jets, wherein a highly relativistic spine outflow is surrounded by a wider and less relativistic sheath outflow. Thermal photons are injected in regions of high optical depth and propagated until the photons escape at the photosphere. Because of the presence of shear in velocity (Lorentz factor) at the boundary of the spine and sheath region, a fraction of the injected photons are accelerated using a Fermi-like acceleration mechanism such that a high-energy power-law tail is formed in the resultant spectrum. We show, in particular, that if a velocity shear with a considerable variance in the bulk Lorentz factor is present, the high-energy part of observed gamma-ray bursts (GRBs) photon spectrum can be explained by this photon acceleration mechanism. We also show that the accelerated photons might also account for the origin of the extra-hard power-law component above the bump of the thermal-like peak seen in some peculiar bursts (e.g., GRB 090510, 090902B, 090926A). We demonstrate that time-integrated spectra can also reproduce the low-energy spectrum of GRBs consistently using a multi-temperature effect when time evolution of the outflow is considered. Last, we show that the empirical E{sub p}-L{sub p} relation can be explained by differences in the outflow properties of individual sources.
Creep of two-phase microstructures for microelectronic applications
NASA Astrophysics Data System (ADS)
Reynolds, Heidi Linch
The mechanical properties of low-melting temperature alloys are highly influenced by their creep behavior. This study investigates the dominant mechanisms that control creep behavior of two-phase, low-melting temperature alloys as a function of microstructure. The alloy systems selected for study were In-Ag and Sn-Bi because their eutectic compositions represent distinctly different microstructures. The In-Ag eutectic contains a discontinuous phase while the Sn-Bi eutectic consists of two continuous phases. In addition, this work generates useful engineering data on Pb-free alloys with a joint specimen geometry that simulates microstructures found in microelectronic applications. The use of joint test specimens allows for observations regarding the practical attainability of superplastic microstructures in real solder joints by varying the cooling rate. Steady-state creep properties of In-Ag eutectic, Sn-Bi eutectic, Sn-xBi solid-solution and pure Bi joints have been measured using constant load tests at temperatures ranging from 0°C to 90°C. Constitutive equations are derived to describe the steady-state creep behavior for In-Ag eutectic solder joints and Sn-xBi solid-solution joints. The data are well represented by an equation of the form proposed by Dorn: a power-law equation applies to each independent creep mechanism. Rate-controlling creep mechanisms, as a function of applied shear stress, test temperature, and joint microstructure, are discussed. Literature data on the steady-state creep properties of Sn-Bi eutectic are reviewed and compared with the Sn-xBi solid-solution and pure Bi joint data measured in the current study. The role of constituent phases in controlling eutectic creep behavior is discussed for both alloy systems. In general, for continuous, two-phase microstructures, where each phase exhibits significantly different creep behavior, the harder or more creep resistant phase will dominate the creep behavior in a lamellar microstructure. If a
[Two-phase Interfaces in Weak External Fields
NASA Technical Reports Server (NTRS)
Percus, J. K.
1996-01-01
Our aim has been that of understanding from first principles the behavior of two-phase interfaces in the absence of gravitational constraints. This is fundamental to our ability to deal with the fluid structures that abound in the real biological, chemical, and physical world. A substantial effort was mounted to determine how familiar hydrodynamic concepts have to be modified and interpreted to make them appropriate to the multi-level structure alluded to above. This was primarily in the context of the microscopic symmetric pressure tensor, which was, for the first time, expressed in the invaluable density functional format, and the used to follow the predictions of popular microscopic models of the energetics of interfacial systems. In the course of these investigations, the previous murky relation between pressure tensor and thermodynamics was completely clarified. The process of extending thermodynamic information to interfacial dynamics was initiated along two paths. One was from the viewpoint of an inertialess lattice gas, resulting in the surprising conclusion that at this level, all transport is governed by precisely the thermodynamic free energy, albeit with a non-trivial effective particle mobility. The other aimed at understanding the fashion in which slow macroscopic motions, accounted for by a time-varying microscopic energy, generate effective hydrodynamic parameters. By examining a solvable model system, it was found that all current procedures for doing so are deficient, and suitable alleviation suggested. The major effect of this project was to set the stage for the analysis of the substantial dynamical regimes in which extensive equilibrium information provides the dominant background. This produces a smooth junction to the models of Araki and Munakata, Giacomin and Lebowitz, and Oxtoby. It is also crucial to our understanding of the complex interfacial equilibrium configurations required for intermediate stages of two-phase separation, for which
Creep of Two-Phase Microstructures for Microelectronic Applications
Reynolds, Heidi Linch
1998-12-01
The mechanical properties of low-melting temperature alloys are highly influenced by their creep behavior. This study investigates the dominant mechanisms that control creep behavior of two-phase, low-melting temperature alloys as a function of microstructure. The alloy systems selected for study were In-Ag and Sn-Bi because their eutectic compositions represent distinctly different microstructure.” The In-Ag eutectic contains a discontinuous phase while the Sn-Bi eutectic consists of two continuous phases. In addition, this work generates useful engineering data on Pb-free alloys with a joint specimen geometry that simulates microstructure found in microelectronic applications. The use of joint test specimens allows for observations regarding the practical attainability of superplastic microstructure in real solder joints by varying the cooling rate. Steady-state creep properties of In-Ag eutectic, Sn-Bi eutectic, Sn-xBi solid-solution and pure Bi joints have been measured using constant load tests at temperatures ranging from O°C to 90°C. Constitutive equations are derived to describe the steady-state creep behavior for In-Ageutectic solder joints and Sn-xBi solid-solution joints. The data are well represented by an equation of the form proposed by Dom: a power-law equation applies to each independent creep mechanism. Rate-controlling creep mechanisms, as a function of applied shear stress, test temperature, and joint microstructure, are discussed. Literature data on the steady-state creep properties of Sn-Bi eutectic are reviewed and compared with the Sn-xBi solid-solution and pure Bi joint data measured in the current study. The role of constituent phases in controlling eutectic creep behavior is discussed for both alloy systems. In general, for continuous, two-phase microstructure, where each phase exhibits significantly different creep behavior, the harder or more creep resistant phase will dominate the creep behavior in a lamellar microstructure. If a
Mixing in confined stratified aquifers
NASA Astrophysics Data System (ADS)
Bolster, Diogo; Valdés-Parada, Francisco J.; LeBorgne, Tanguy; Dentz, Marco; Carrera, Jesus
2011-03-01
Spatial variability in a flow field leads to spreading of a tracer plume. The effect of microdispersion is to smooth concentration gradients that exist in the system. The combined effect of these two phenomena leads to an 'effective' enhanced mixing that can be asymptotically quantified by an effective dispersion coefficient (i.e. Taylor dispersion). Mixing plays a fundamental role in driving chemical reactions. However, at pre-asymptotic times it is considerably more difficult to accurately quantify these effects by an effective dispersion coefficient as spreading and mixing are not the same (but intricately related). In this work we use a volume averaging approach to calculate the concentration distribution of an inert solute release at pre-asymptotic times in a stratified formation. Mixing here is characterized by the scalar dissipation rate, which measures the destruction of concentration variance. As such it is an indicator for the degree of mixing of a system. We study pre-asymptotic solute mixing in terms of explicit analytical expressions for the scalar dissipation rate and numerical random walk simulations. In particular, we divide the concentration field into a mean and deviation component and use dominant balance arguments to write approximate governing equations for each, which we then solve analytically. This allows us to explicitly evaluate the separate contributions to mixing from the mean and the deviation behavior. We find an approximate, but accurate expression (when compared to numerical simulations) to evaluate mixing. Our results shed some new light on the mechanisms that lead to large scale mixing and allow for a distinction between solute spreading, represented by the mean concentration, and mixing, which comes from both the mean and deviation concentrations, at pre-asymptotic times.
NASA Astrophysics Data System (ADS)
Young, Eric Paul
Two-phase flow in helical conduits is important in many industries where reaction between components, heat transfer, and mass transport are utilized as processes. The helical design is chosen for the effects of secondary flow patterns that reduce axial dispersion, increased heat transfer, and also their compact design. The first is a result of the secondary flow, which continually transports fluid from the near wall region to the bulk of the flow. In single-phase chemical reactor design this secondary flow increases radial mixing and reduces axial dispersion. In heat exchanger design it increases laminar heat transfer while extending the Reynolds number range of laminar flow. A literature review of the work on helical pipe flow shows that the vast majority of the work is on toroidal single-phase flow, and analyses of two-phase flow are sparse. This dissertation addresses this void by presenting an analytical model of the stratified and annular flow regime transitions in helical conduits, by consideration of the governing equations and mechanisms for transition in the toroidal geometry including the major impact of pitch. Studies have taken a similar approach for straight inclined horizontal and vertical geometries, but none have been found which resolve two-phase flow in the curved geometry of a helix. The main issue in resolving the flow in this geometry is that of determining appropriate inter-phase momentum transfer, and the appropriate friction correlations for wall interaction. These issues are resolved to yield a novel attempt at modeling helical two-phase flow. Pitch is considered negligible in introduction of torsion, while the dominating influence of the centrifugal force is retained. The formulation of the governing equations are taken from a general vector form that is readily extended to a true helix that includes torsion. The predictive capability of the current model is compared to the data and observations of the two-phase helical flow studies
Passive Two-Phase Cooling of Automotive Power Electronics: Preprint
Moreno, G.; Jeffers, J. R.; Narumanchi, S.; Bennion, K.
2014-08-01
Experiments were conducted to evaluate the use of a passive two-phase cooling strategy as a means of cooling automotive power electronics. The proposed cooling approach utilizes an indirect cooling configuration to alleviate some reliability concerns and to allow the use of conventional power modules. An inverter-scale proof-of-concept cooling system was fabricated, and tests were conducted using the refrigerants hydrofluoroolefin HFO-1234yf and hydrofluorocarbon HFC-245fa. Results demonstrated that the system can dissipate at least 3.5 kW of heat with 250 cm3 of HFC-245fa. An advanced evaporator design that incorporates features to improve performance and reduce size was conceived. Simulation results indicate its thermal resistance can be 37% to 48% lower than automotive dual side cooled power modules. Tests were also conducted to measure the thermal performance of two air-cooled condensers--plain and rifled finned tube designs. The results combined with some analysis were then used to estimate the required condenser size per operating conditions and maximum allowable system (i.e., vapor and liquid) temperatures.
An automated two-phase system for hydrogel microbead production.
Coutinho, Daniela F; Ahari, Amir F; Kachouie, Nezamoddin N; Gomes, Manuela E; Neves, Nuno M; Reis, Rui L; Khademhosseini, Ali
2012-09-01
Polymeric beads have been used for protection and delivery of bioactive materials, such as drugs and cells, for different biomedical applications. Here, we present a generic two-phase system for the production of polymeric microbeads of gellan gum or alginate, based on a combination of in situ polymerization and phase separation. Polymer droplets, dispensed using a syringe pump, formed polymeric microbeads while passing through a hydrophobic phase. These were then crosslinked, and thus stabilized, in a hydrophilic phase as they crossed through the hydrophobic-hydrophilic interface. The system can be adapted to different applications by replacing the bioactive material and the hydrophobic and/or the hydrophilic phases. The size of the microbeads was dependent on the system parameters, such as needle size and solution flow rate. The size and morphology of the microbeads produced by the proposed system were uniform, when parameters were kept constant. This system was successfully used for generating polymeric microbeads with encapsulated fluorescent beads, cell suspensions and cell aggregates proving its ability for generating bioactive carriers that can potentially be used for drug delivery and cell therapy.
Particle clustering within a two-phase turbulent pipe jet
NASA Astrophysics Data System (ADS)
Lau, Timothy; Nathan, Graham
2016-11-01
A comprehensive study of the influence of Stokes number on the instantaneous distributions of particles within a well-characterised, two-phase, turbulent pipe jet in a weak co-flow was performed. The experiments utilised particles with a narrow size distribution, resulting in a truly mono-disperse particle-laden jet. The jet Reynolds number, based on the pipe diameter, was in the range 10000 <= ReD <= 40000 , while the exit Stokes number was in the range 0 . 3 <= SkD <= 22 . 4 . The particle mass loading was fixed at ϕ = 0 . 4 , resulting in a flow that was in the two-way coupling regime. Instantaneous particle distributions within a two-dimensional sheet was measured using planar nephelometry while particle clusters were identified and subsequently characterised using an in-house developed technique. The results show that particle clustering is significantly influenced by the exit Stokes number. Particle clustering was found to be significant for 0 . 3 <= SkD <= 5 . 6 , with the degree of clustering increasing as SkD is decreased. The clusters, which typically appeared as filament-like structures with high aspect ratio oriented at oblique angles to the flow, were measured right from the exit plane, suggesting that they were generated inside the pipe. The authors acknowledge the financial contributions by the Australian Research Council (Grant No. DP120102961) and the Australian Renewable Energy Agency (Grant No. USO034).
Unsteady flow analysis of a two-phase hydraulic coupling
NASA Astrophysics Data System (ADS)
Hur, N.; Kwak, M.; Lee, W. J.; Moshfeghi, M.; Chang, C.-S.; Kang, N.-W.
2016-06-01
Hydraulic couplings are being widely used for torque transmitting between separate shafts. A mechanism for controlling the transmitted torque of a hydraulic system is to change the amount of working fluid inside the system. This paper numerically investigates three-dimensional turbulent flow in a real hydraulic coupling with different ratios of charged working fluid. Working fluid is assumed to be water and the Realizable k-ɛ turbulence model together with the VOF method are used to investigate two-phase flow inside the wheels. Unsteady simulations are conducted using the sliding mesh technique. The primary wheel is rotating at a fixed speed of 1780 rpm and the secondary wheel rotates at different speeds for simulating different speed ratios. Results are investigated for different blade angles, speed ratios and also different water volume fractions, and are presented in the form of flow patterns, fluid average velocity and also torques values. According to the results, blade angle severely affects the velocity vector and the transmitted torque. Also in the partially-filled cases, air is accumulated in the center of the wheel forming a toroidal shape wrapped by water and the transmitted torque sensitively depends on the water volume fraction. In addition, in the fully-filled case the transmitted torque decreases as the speed ration increases and the average velocity associated with lower speed ratios are higher.
Cryogenic Two-Phase Flight Experiment: Results overview
NASA Technical Reports Server (NTRS)
Swanson, T.; Buchko, M.; Brennan, P.; Bello, M.; Stoyanof, M.
1995-01-01
This paper focuses on the flight results of the Cryogenic Two-Phase Flight Experiment (CRYOTP), which was a Hitchhiker based experiment that flew on the space shuttle Columbia in March of 1994 (STS-62). CRYOTP tested two new technologies for advanced cryogenic thermal control; the Space Heat Pipe (SHP), which was a constant conductance cryogenic heat pipe, and the Brilliant Eyes Thermal Storage Unit (BETSU), which was a cryogenic phase-change thermal storage device. These two devices were tested independently during the mission. Analysis of the flight data indicated that the SHP was unable to start in either of two attempts, for reasons related to the fluid charge, parasitic heat leaks, and cryocooler capacity. The BETSU test article was successfully operated with more than 250 hours of on-orbit testing including several cooldown cycles and 56 freeze/thaw cycles. Some degradation was observed with the five tactical cryocoolers used as thermal sinks, and one of the cryocoolers failed completely after 331 hours of operation. Post-flight analysis indicated that this problem was most likely due to failure of an electrical controller internal to the unit.
Sound speed criterion for two-phase critical flow
NASA Astrophysics Data System (ADS)
Chung, M.-S.; Park, S.-B.; Lee, H.-K.
2004-09-01
Critical flow simulation for non-homogeneous, non-equilibrium two-phase flows is improved by applying a new sound speed model which is derived from the characteristic analysis of hyperbolic two-fluid model. The hyperbolicity of two-fluid model was based on the concept of surface tension for the interfacial pressure jump terms in the momentum equations. Real eigenvalues obtained as the closed-form solution of characteristic polynomial represent the sound speeds in the bubbly flow regime that agree well with the existing experimental data. The analytic sound speed is consistent with that obtained by the earlier study of Nguyen et al. though there is a difference between them especially in the limiting condition. The present sound speed shows more reasonable result in that condition than Nguyen et al.'s does. The present critical flow criterion derived by the present sound speed is employed in the MARS code and is assessed by treating several nozzle flow tests. The assessment results, without any adjustment made by some discharge coefficients, demonstrate more accurate predictions of critical flow rate than those of the earlier critical flow calculations in the bubbly flow regime.
Passive Two-Phase Cooling for Automotive Power Electronics
Moreno, G.; Jeffers, J. R.; Narumanchi, S.; Bennion, K.
2014-01-01
Experiments were conducted to evaluate the use of a passive two-phase cooling strategy as a means of cooling automotive power electronics. The proposed cooling approach utilizes an indirect cooling configuration to alleviate some reliability concerns and to allow the use of conventional power modules. An inverter-scale proof-of-concept cooling system was fabricated and tested using the refrigerants hydrofluoroolefin HFO-1234yf and hydrofluorocarbon HFC-245 fa. Results demonstrated that the system can dissipate at least 3.5 kW of heat with 250 cm3 of HFC-245fa. An advanced evaporator concept that incorporates features to improve performance and reduce its size was designed. Simulation results indicate the concept's thermal resistance can be 58% to 65% lower than automotive dual-side-cooled power modules. Tests were also conducted to measure the thermal performance of two air-cooled condensers-plain and rifled finned tube designs. The results combined with some analysis were then used to estimate the required condenser size per operating conditions and maximum allowable system (i.e., vapor and liquid) temperatures.
A turbulent two-phase flow model for nebula flows
NASA Technical Reports Server (NTRS)
Champney, Joelle M.; Cuzzi, Jeffrey N.
1990-01-01
A new and very efficient turbulent two-phase flow numericaly model is described to analyze the environment of a protoplanetary nebula at a stage prior to the formation of planets. Focus is on settling processes of dust particles in flattened gaseous nebulae. The model employs a perturbation technique to improve the accuracy of the numerical simulations of such flows where small variations of physical quantities occur over large distance ranges. The particles are allowed to be diffused by gas turbulence in addition to settling under gravity. Their diffusion coefficients is related to the gas turbulent viscosity by the non-dimensional Schmidt number. The gas turbulent viscosity is determined by the means of the eddy viscosity hypothesis that assumes the Reynolds stress tensor proportional to the mean strain rate tensor. Zero- and two-equation turbulence models are employed. Modeling assumptions are detailed and discussed. The numerical model is shown to reproduce an existing analytical solution for the settling process of particles in an inviscid nebula. Results of nebula flows are presented taking into account turbulence effects of nebula flows. Diffusion processes are found to control the settling of particles.
A two-phase code for protoplanetary disks
NASA Astrophysics Data System (ADS)
Inaba, S.; Barge, P.; Daniel, E.; Guillard, H.
2005-02-01
A high accuracy 2D hydrodynamical code has been developed to simulate the flow of gas and solid particles in protoplanetary disks. Gas is considered as a compressible fluid while solid particles, fully coupled to the gas by aerodynamical forces, are treated as a pressure-free diluted second phase. The solid particles lose energy and angular momentum which are transfered to the gas. As a result particles migrate inward toward the star and gas moves outward. High accuracy is necessary to account for the coupling. Boundary conditions must account for the inward/outward motions of the two phases. The code has been tested on one and two dimensional situations. The numerical results were compared with analytical solutions in three different cases: i) the disk is composed of a single gas component; ii) solid particles migrate in a steady flow of gas; iii) gas and solid particles evolve simultaneously. The code can easily reproduce known analytical solutions and is a powerful tool to study planetary formation at the decoupling stage. For example, the evolution of an over-density in the radial distribution of solids is found to differ significantly from the case where no back reaction of the particles onto the gas is assumed. Inside the bump, solid particles have a drift velocity approximately 16 times smaller than outside which significantly increases the residence time of the particles in the nebula. This opens some interesting perspectives to solve the timescale problem for the formation of planetesimals.
Particle migration in two-phase, viscoelastic flows
NASA Astrophysics Data System (ADS)
Jaensson, Nick; Hulsen, Martien; Anderson, Patrick
2014-11-01
Particles suspended in creeping, viscoelastic flows can migrate across stream lines due to gradients in normal stresses. This phenomenon has been investigated both numerically and experimentally. However, particle migration in the presence of fluid-fluid interfaces is hardly studied. We present results of simulations in 2D and 3D of rigid spherical particles in two-phase flows, where either one or both of the fluids are viscoelastic. The fluid-fluid interface is assumed to be diffuse and is described using Cahn-Hilliard theory. The particle boundary is assumed to be sharp and is described by a boundary-fitted, moving mesh. The governing equations are solved using the finite element method. We show that differences in normal stresses between the two fluids can induce a migration of the particle towards the interface in a shear flow. Depending on the magnitude of the surface tension and the properties of the fluids, particle migration can be halted due to the induced Laplace pressure, the particle can be adsorbed at the interface, or the particle can cross the interface into the other fluid. Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
Turbulent transition modification in dispersed two-phase pipe flow
NASA Astrophysics Data System (ADS)
Winters, Kyle; Longmire, Ellen
2014-11-01
In a pipe flow, transition to turbulence occurs at some critical Reynolds number, Rec , and transition is associated with intermittent swirling structures extending over the pipe cross section. Depending on the magnitude of Rec , these structures are known either as puffs or slugs. When a dispersed second liquid phase is added to a liquid pipe flow, Rec can be modified. To explore the mechanism for this modification, an experiment was designed to track and measure these transitional structures. The facility is a pump-driven circuit with a 9m development and test section of diameter 44mm. Static mixers are placed upstream to generate an even dispersion of silicone oil in a water-glycerine flow. Pressure signals were used to identify transitional structures and trigger a high repetition rate stereo-PIV system downstream. Stereo-PIV measurements were obtained in planes normal to the flow, and Taylor's Hypothesis was employed to infer details of the volumetric flow structure. The presentation will describe the sensing and imaging methods along with preliminary results for the single and two-phase flows. Supported by Nanodispersions Technology.
How stratified is mantle convection?
NASA Astrophysics Data System (ADS)
Puster, Peter; Jordan, Thomas H.
1997-04-01
due to slabs alone. A stratification index, Sƒ≲0.2, is sufficient to exclude many stratified convection models still under active consideration, including most forms of chemical layering between the upper and lower mantle, as well as the more extreme versions of avalanching convection governed by a strong endothermic phase change.
Waves in Turbulent Stably Stratified Shear Flow
NASA Technical Reports Server (NTRS)
Jacobitz, F. G.; Rogers, M. M.; Ferziger, J. H.; Parks, John W. (Technical Monitor)
2002-01-01
Two approaches for the identification of internal gravity waves in sheared and unsheared homogeneous stratified turbulence are investigated. First, the phase angle between the vertical velocity and density fluctuations is considered. It was found, however, that a continuous distribution of the phase angle is present in weakly and strongly stratified flow. Second, a projection onto the solution of the linearized inviscid equations of motion of unsheared stratified flow is investigated. It was found that a solution of the fully nonlinear viscous Navier-Stokes equations can be represented by the linearized inviscid solution. The projection yields a decomposition into vertical wave modes and horizontal vortical modes.
Dense Heterogeneous Continuum Model of Two-Phase Explosion Fields
Kuhl, A L; Bell, J B
2010-04-07
A heterogeneous continuum model is proposed to describe the dispersion of a dense Aluminum particle cloud in an explosion. Let {alpha}{sub 1} denote the volume fraction occupied by the gas and {alpha}{sub 2} the fraction occupied by the solid, satisfying the volume conservation relation: {alpha}{sub 1} + {alpha}{sub 2} = 1. When the particle phase occupies a non-negligible volume fraction (i.e., {alpha}{sub 2} > 0), additional terms, proportional to {alpha}{sub 2}, appear in the conservation laws for two-phase flows. These include: (i) a particle pressure (due to particle collisions), (ii) a corresponding sound speed (which produces real eigenvalues for the particle phase system), (iii) an Archimedes force induced on the particle phase (by the gas pressure gradient), and (iv) multi-particle drag effects (which enhance the momentum coupling between phases). These effects modify the accelerations and energy distributions in the phases; we call this the Dense Heterogeneous Continuum Model. A characteristics analysis of the Model equations indicates that the system is hyperbolic with real eigenvalues for the gas phase: {l_brace}v{sub 1}, v{sub 1} {+-} {alpha}{sub 1}{r_brace} and for the 'particle gas' phase: {l_brace}v{sub 2}, v{sub 2} {+-}{alpha}{sub 2}{r_brace} and the particles: {l_brace}v{sub 2}{r_brace}, where v{sub i} and {alpha}{sub i} denote the velocity vector and sound speed of phase i. These can be used to construct a high-order Godunov scheme to integrate the conservation laws of a dense heterogeneous continuum.
Tobacco protein separation by aqueous two-phase extraction.
Balasubramaniam, Deepa; Wilkinson, Carol; Van Cott, Kevin; Zhang, Chenming
2003-03-07
Tobacco has long been considered as a host to produce large quantity of high-valued recombinant proteins. However, dealing with large quantities of biomass is a challenge for downstream processing. Aqueous two-phase extraction (ATPE) has been widely used in purifying proteins from various sources. It is a protein-friendly process and can be scaled up easily. In this paper, ATPE was studied for its applicability to recombinant protein purification from tobacco with egg white lysozyme as the model protein. Separate experiments with poly(ethylene glycol) (PEG)-salt-tobacco extract and PEG-salt-lysozyme were carried out to determine the partition behavior of tobacco protein and lysozyme, respectively. Two-level fractional factorial designs were used to study the effects of factors such as, PEG molecular mass, PEG concentration, the concentration of phase forming salt, sodium chloride concentration and pH, on protein partitioning. The results showed that, among the studied systems, PEG-sodium sulfate system was most suitable for lysozyme purification. Detailed experiments were conducted by spiking lysozyme into the tobacco extract. The conditions with highest selectivity of lysozyme over native tobacco protein were determined using a response surface design. The purification factor was further improved by decreasing the phase ratio along the tie line corresponding to the phase compositions with the highest selectivity. Under selected conditions the lysozyme yield was predicted to be 87% with a purification factor of 4 and concentration factor of 14. From this study, ATPE was shown to be suitable for initial protein recovery and partial purification from transgenic tobacco.
Two Phase Flow Mapping and Transition Under Microgravity Conditions
NASA Technical Reports Server (NTRS)
Parang, Masood; Chao, David F.
1998-01-01
In this paper, recent microgravity two-phase flow data for air-water, air-water-glycerin, and air- water-Zonyl FSP mixtures are analyzed for transition from bubbly to slug and from slug to annular flow. It is found that Weber number-based maps are inadequate to predict flow-pattern transition, especially over a wide range of liquid flow rates. It is further shown that slug to annular flow transition is dependent on liquid phase Reynolds number at high liquid flow rate. This effect may be attributed to growing importance of liquid phase inertia in the dynamics of the phase flow and distribution. As a result a new form of scaling is introduced to present data using liquid Weber number based on vapor and liquid superficial velocities and Reynolds number based on liquid superficial velocity. This new combination of the dimensionless parameters seem to be more appropriate for the presentation of the microgravity data and provides a better flow pattern prediction and should be considered for evaluation with data obtained in the future. Similarly, the analysis of bubble to slug flow transition indicates a strong dependence on both liquid inertia and turbulence fluctuations which seem to play a significant role on this transition at high values of liquid velocity. A revised mapping of data using a new group of dimensionless parameters show a better and more consistent description of flow transition over a wide range of liquid flow rates. Further evaluation of the proposed flow transition mapping will have to be made after a wider range of microgravity data become available.
Two-phase transformation of lepidocrocite to maghemite
NASA Astrophysics Data System (ADS)
Dekkers, M. J.; Gapeev, A. K.; Gendler, T. S.; Gribov, S. K.; Shcherbakov, V. P.
2003-04-01
A detailed investigation of CRM acquired at different stages of the transformation lepidocrocite -> maghemite -> hematite is carried out. Apparently, at least two-stage lepidocrocite maghemite transformation was revealed from: a) the two-peak Ms(T) curve; b) the observation of constricted hysteresis loops appearing after annealing fresh lepidocrocite samples at elevated temperatures; c) continuous monitoring (for 500 hrs) of CRM acquisition at elevated temperatures. For the latter two sets of CRM acquisition experiments at 12 temperatures from 175C to 550C in the presence of 0.1 mT magnetic field were performed: 1) with fine dispersed natural lepidocrocite grains in a kaolin matrix (about 1 volume % of lepidocrocite), 2) for lepidocrocite peaces 3x3x3 mm in size. In both cases the CRM was detected already at 175C after 1 day of annealing. Note that this temperature is lower than the temperature of the TGA peak of the lepidocrocite -> maghemite transformation. Mossbauer spectra obtained from the peaces after annealing at 225C during 6 and 14 hours, respectively, revealed significantly different patterns. Unexpectadly, fine dispersed maghemite grains formed due the lepidocrocite dehydration in the first peace (6 hrs of annealing) occurred to be more ordered than those of from the second peace. The samples are subjected to the X-ray analysis in an attempt to clarify the observed difference. The observed phenomena can be explained by the two-phase conception of the transformation lepidocrocite -> maghemite. First the precipitation of small superparamagnetic particles of maghemite takes place growing with time. Second, these grains coalesce with each other resulting in appearance of the antiphase boundaries decreasing the susceptibility, slowing down the process of CRM acquisition and generating the constricted hysteresis loops. The work is supported by INTAS 99-1273.
Two phase damage theory and the failure enveloppes of sandstone
NASA Astrophysics Data System (ADS)
Ricard, Y.; Bercovici, D.
2003-04-01
Using a classical averaging approach, we derive a two-phase theory to describe the deformation of a porous material made of a matrix containing voids. The presence and evolution of surface energy at the interface between the solid matrix and voids is taken into account with non-equilibrium thermodynamic considerations that allow storage of deformational work as surface energy on growing or newly created voids. This treatment leads to a simple description of isotropic damage that can be applied to low-cohesion media such as sandstone. In particular, the theory yields two possible solutions wherein samples can either ``break" by shear localization with dilation (i.e., void creation), or undergo shear-enhanced compaction (void collapse facilitated by deviatoric stress). For a given deviatoric stress and confining pressure, the dominant solution is the one with the largest absolute value of the dilation rate, |Γ|, which thus predicts that shear-localization and dilation occur at low effective pressures, while shear-enhanced compaction occurs at larger effective pressure. Stress trajectories of constant |Γ| represent potential failure envelopes that are ogive (Gothic-arch) shaped curves wherein the ascending branch represents failure by dilation and shear-localization, and the descending branch denotes shear-enhanced compactive failure. The theory further predicts that the onset of dilation preceding shear-localization and failure necessarily occurs at the transition from compactive to dilational states and thus along a line connecting the peaks of constant-|Γ| ogives. Finally, the theory implies that while shear-enhanced compaction first occurs with increasing deviatoric stress (at large effective pressure), dilation will occur at higher deviatoric stresses. All these predictions in fact compare very successfully with various experimental data. Indeed, the theory leads to a normalization where all the data of failure envelopes and dilation thresholds collapse to a
Investigation of two-phase flow processes in coal slurry/hydrogen heaters. Final report
Sam, R.G.; Crowley, C.J.
1986-08-01
Experimental and analytical results are presented for two-phase slug flow in a horizontal, transparent pipe at large diameter (6.75 in.) at high gas density (20 times the density of air at atmospheric pressure) and at liquid viscosities ranging from 1 to 1000 centipoise. The test section replicates 1 1/2 rectangular coils (40 ft by 10 ft) of a fired heater in a coal liquefaction plant. Regime transtion, pressure drop, void fraction, and slug characteristic data have been obtained for liquid superficial velocities ranging from 0.2 to 6 ft/s and gas superficial velocities ranging from 0.2 to 12 ft/s. Regime transition results have been compared with the Taitel-Dukler analytical flow regime map. The transition from stratified to slug flow, which is underpredicted by the original analysis, has been studied in particular. Comparison with the dimensionless transition criterion (gas Froude number) shows that increased liquid viscosity increases the liquid level at which the transition occurs. Pressure drop data at the transition have been used to evaluate the interfacial shear and to show that it is greater than is assumed in the Taitel-Dukler analysis. Sensitivity studies for the transition criterion and interfacial shear illustrate exactly why the transition is underpredicted on the flow regime map and how the predictions can be improved. Photos of the flow patterns illustrate the mechanism of slug formation at high viscosity compared with low viscosity. Pressure drop, void fraction, and slug characteristic results are compared with an analysis for pressure drop in slug flow, demonstrating better predictive capability of this model at large pipe size, high gas density, and high viscosity, compared with correlations from the literature. The pressure drop model is also shown to be in excellent agreement with coal liquefaction pilot plant data. 34 refs.
Magnetized stratified rotating shear waves.
Salhi, A; Lehner, T; Godeferd, F; Cambon, C
2012-02-01
stability of the solution at infinite vertical wavelength (k(3) = 0): There is an oscillatory behavior for τ > 1+|K(2)/k(1)|, where τ = St is a dimensionless time and K(2) is the radial component of the wave vector at τ = 0. The model is suitable to describe instabilities leading to turbulence by the bypass mechanism that can be relevant for the analysis of magnetized stratified Keplerian disks with a purely azimuthal field. For initial isotropic conditions, the time evolution of the spectral density of total energy (kinetic + magnetic + potential) is considered. At k(3) = 0, the vertical motion is purely oscillatory, and the sum of the vertical (kinetic + magnetic) energy plus the potential energy does not evolve with time and remains equal to its initial value. The horizontal motion can induce a rapid transient growth provided K(2)/k(1)>1. This rapid growth is due to the aperiodic velocity vortex mode that behaves like K(h)/k(h) where k(h)(τ)=[k(1)(2) + (K(2) - k(1)τ)(2)](1/2) and K(h) =k(h)(0). After the leading phase (τ > K(2)/k(1)>1), the horizontal magnetic energy and the horizontal kinetic energy exhibit a similar (oscillatory) behavior yielding a high level of total energy. The contribution to energies coming from the modes k(1) = 0 and k(3) = 0 is addressed by investigating the one-dimensional spectra for an initial Gaussian dense spectrum. For a magnetized Keplerian disk with a purely vertical field, it is found that an important contribution to magnetic and kinetic energies comes from the region near k(1) = 0. The limit at k(1) = 0 of the streamwise one-dimensional spectra of energies, or equivalently, the streamwise two-dimensional (2D) energy, is then computed. The comparison of the ratios of these 2D quantities with their three-dimensional counterparts provided by previous direct numerical simulations shows a quantitative agreement.
Turbulence Modeling in Stratified Flows over Topography
2007-09-30
Details of the basic LES model can be found in Armenio and Sarkar [1]. To avoid the need to resolve the very small turbulent motions near the lower... Armenio and S. Sarkar. An investigation of stably stratified turbulent channel flow using large-eddy simulation. J. Fluid Mech., 459:1–42, 2002. [2...276, 1994. [12] J. Taylor, S. Sarkar, and V. Armenio . An investigation of stably stratified turbulent channel flow using large-eddy simulation. Phys
Radiative transfer in a plane stratified dielectric
NASA Technical Reports Server (NTRS)
Wilheit, T. T., Jr.
1975-01-01
A model is developed for calculating radiative transfer in a stratified dielectric. This model is used to show that the reflectivity of a stratified dielectric is primarily determined by gradients in the real part of the refractive index over distances on the order of 1/10 wavelength in the medium. The effective temperature of the medium is determined by the thermodynamic temperature profile over distances of the order delta T.
Two-phase analysis in consensus genetic mapping.
Ronin, Y; Mester, D; Minkov, D; Belotserkovski, R; Jackson, B N; Schnable, P S; Aluru, S; Korol, A
2012-05-01
Numerous mapping projects conducted on different species have generated an abundance of mapping data. Consequently, many multilocus maps have been constructed using diverse mapping populations and marker sets for the same organism. The quality of maps varies broadly among populations, marker sets, and software used, necessitating efforts to integrate the mapping information and generate consensus maps. The problem of consensus genetic mapping (MCGM) is by far more challenging compared with genetic mapping based on a single dataset, which by itself is also cumbersome. The additional complications introduced by consensus analysis include inter-population differences in recombination rate and exchange distribution along chromosomes; variations in dominance of the employed markers; and use of different subsets of markers in different labs. Hence, it is necessary to handle arbitrary patterns of shared sets of markers and different level of mapping data quality. In this article, we introduce a two-phase approach for solving MCGM. In phase 1, for each dataset, multilocus ordering is performed combined with iterative jackknife resampling to evaluate the stability of marker orders. In this phase, the ordering problem is reduced to the well-known traveling salesperson problem (TSP). Namely, for each dataset, we look for order that gives minimum sum of recombination distances between adjacent markers. In phase 2, the optimal consensus order of shared markers is selected from the set of allowed orders and gives the minimal sum of total lengths of nonconflicting maps of the chromosome. This criterion may be used in different modifications to take into account the variation in quality of the original data (population size, marker quality, etc.). In the foregoing formulation, consensus mapping is considered as a specific version of TSP that can be referred to as "synchronized TSP." The conflicts detected after phase 1 are resolved using either a heuristic algorithm over the
48 CFR 36.301 - Use of two-phase design-build selection procedures.
Code of Federal Regulations, 2010 CFR
2010-10-01
... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Use of two-phase design... ACQUISITION REGULATION SPECIAL CATEGORIES OF CONTRACTING CONSTRUCTION AND ARCHITECT-ENGINEER CONTRACTS Two-Phase Design-Build Selection Procedures 36.301 Use of two-phase design-build selection procedures....
48 CFR 570.105-2 - Two-phase design-build selection procedures.
Code of Federal Regulations, 2010 CFR
2010-10-01
... 48 Federal Acquisition Regulations System 4 2010-10-01 2010-10-01 false Two-phase design-build..., you must use the two-phase design-build selection procedures in section 303M of the Federal Property... use of the two-phase selection procedures. (v) The capability of the agency to manage the...
48 CFR 570.305 - Two-phase design-build selection procedures.
Code of Federal Regulations, 2010 CFR
2010-10-01
... 48 Federal Acquisition Regulations System 4 2010-10-01 2010-10-01 false Two-phase design-build... for Leasehold Interests in Real Property 570.305 Two-phase design-build selection procedures. (a) These procedures apply to acquisitions of leasehold interests if you use the two-phase...
Stratified charge rotary engine for general aviation
NASA Technical Reports Server (NTRS)
Mount, R. E.; Parente, A. M.; Hady, W. F.
1986-01-01
A development history, a current development status assessment, and a design feature and performance capabilities account are given for stratified-charge rotary engines applicable to aircraft propulsion. Such engines are capable of operating on Jet-A fuel with substantial cost savings, improved altitude capability, and lower fuel consumption by comparison with gas turbine powerplants. Attention is given to the current development program of a 400-hp engine scheduled for initial operations in early 1990. Stratified charge rotary engines are also applicable to ground power units, airborne APUs, shipboard generators, and vehicular engines.
Reinemann, D J
1996-12-01
Most pipeline systems in dairy and food processing plants are cleaned by circulating cleaning solutions under pressure with a liquid pump. The flow of the circulated solutions is single-phase or flooded flow. Milking system pipelines are subject to special requirements which distinguish them from those in dairy and other food processing plants. Milking system pipelines are considerably larger in diameter than product lines in dairy plants because they must carry both milk and air in a stratified flow condition during the milking process. Milking machine Clean-In-Place (CIP) systems have historically used flooded flow to circulate cleaning solutions. The force to move liquid, however, is typically the vacuum provided by the same vacuum pump used during milking, rather than a positive pressure liquid pump. As the size and complexity of milking machines has increased in recent years, flooded flow CIP systems have become inadequate. The amount of water required to fully flood a milking system becomes impractical with very long and/or large diameter pipelines. The power available to achieve adequate flow velocity is also limited. Air admission has been used to produce two-phase (air/water) slug flow and overcome some of the limitations of fully flooded CIP. Cycled air admission can reduce the amount of water required for circulation and increase flow velocities and thus enhance mechanical cleaning action. Cycled air admission has been implemented in the field largely through trial and error methods. There has been a lack of fundamental design information and testing protocols for air-injected milking machine CIP systems. This has resulted in mixed success in the application of air injected systems. This paper summarizes both laboratory and field research conducted at the University of Wisconsin Milking Research and Instruction lab to provide basic information for the design of air injected CIP systems and methods for field assessment of these systems. Just as properly
Two-Phase Annular Flow in Helical Coil Flow Channels in a Reduced Gravity Environment
NASA Technical Reports Server (NTRS)
Keshock, Edward G.; Lin, Chin S.
1996-01-01
A brief review of both single- and two-phase flow studies in curved and coiled flow geometries is first presented. Some of the complexities of two-phase liquid-vapor flow in curved and coiled geometries are discussed, and serve as an introduction to the advantages of observing such flows under a low-gravity environment. The studies proposed -- annular two-phase air-water flow in helical coil flow channels are described. Objectives of the studies are summarized.
A chaotic system of two-phase flow in a small, horizontal, rectangular channel
Cai, Y.; Wambsganss, M.W.; Jendrzejczyk, J.A.
1995-07-01
Various measurement tools that are used in chaos theory were applied to analyze two-phase pressure signals with the objective of identifying and interpreting flow pattern transitions for two-phase flows in a small, horizontal rectangular channel. These measurement tools included power spectral density function, autocorrelation function, pseudo-phase-plane trajectory, Lyapunov exponents, and fractal dimensions. It was demonstrated that the randomlike pressure fluctuations characteristic of two-phase flow in small rectangular channels are chaotic. As such, they are governed by a high-order deterministic system. The correlation dimension is potentially a new approach for identifying certain two-phase flow patterns and transitions.
Fusion Research of Electrical Tomography with Other Sensors for Two-phase Flow Measurement
NASA Astrophysics Data System (ADS)
Deng, Xiang; Yang, W. Q.
2012-01-01
The two-phase flow widely exists in the nature and industrial processes. The measurement of two-phase flows, including gas/solids, gas/liquid and liquid/liquid flows, is still challenging. Fusions of electrical tomography with conventional sensors provide possibilities to improve two-phase flow accurate measurement. In this paper, fusions of (1) electrical resistance tomography (ERT) with electromagnetic (EM) flowmeter, (2) electrical capacitance tomography (ECT) with ERT and (3) ECT with electrostatic sensor are introduced. Some research results of fusion methods are presented and discussed. This paper can provide the theoretical support for the multi-sensor fusion for two-phase flow measurement.
Zeng, Chao-Xi; Xin, Rui-Pu; Qi, Sui-Jian; Yang, Bo; Wang, Yong-Hua
2016-02-01
Aqueous two-phase systems, based on the use of natural quaternary ammonium compounds, were developed to establish a benign biotechnological route for efficient protein separation. In this study, aqueous two-phase systems of two natural resources betaine and choline with polyethyleneglycol (PEG400/600) or inorganic salts (K2 HPO4 /K3 PO4 ) were formed. It was shown that in the K2 HPO4 -containing aqueous two-phase system, hydrophobic interactions were an important driving force of protein partitioning, while protein size played a vital role in aqueous two-phase systems that contained polyethylene glycol. An extraction efficiency of more than 90% for bovine serum albumin in the betaine/K2 HPO4 aqueous two-phase system can be obtained, and this betaine-based aqueous two-phase system provided a gentle and stable environment for the protein. In addition, after investigation of the cluster phenomenon in the betaine/K2 HPO4 aqueous two-phase systems, it was suggested that this phenomenon also played a significant role for protein extraction in this system. The development of aqueous two-phase systems based on natural quaternary ammonium compounds not only provided an effective and greener method of aqueous two-phase system to meet the requirements of green chemistry but also may help to solve the mystery of the compartmentalization of biomolecules in cells.
Analysis of two-phase flow included vibrations in piping systems
Hiramatsu, T.; Komura, Y.; Yano, S.
1982-01-01
The purpose of this analysis is to predict the vibration level of a pipe conveying a two-phase flowing fluid. Experiments were carried out with a horizontally supported U-type piping system, conveying an air-water two-phase flow in a steady state condition. A theoretical analysis is achieved using the transfer method for vibration responses of the system excited by the forces of traveling liquid piston and the momentum change of two-phase flow. Comparing experimental and theoretical studies, the author concluded that the vibrational behavior of piping systems conveying two-phase flowing fluid can be predicted quantitatively. 8 refs.
Oscillations in a Linearly Stratified Salt Solution
ERIC Educational Resources Information Center
Heavers, Richard M.
2007-01-01
Our physics students like to watch a ball bouncing underwater. They do this by dropping a weighted plastic ball into a 1000-ml cylinder filled with a linearly stratified salt-water solution at room temperature. The ball oscillates and comes to rest at about mid-depth. Its motion is analogous to the damped vertical oscillations of a mass hanging…
The Stratified Adaptive Computerized Ability Test.
ERIC Educational Resources Information Center
Weiss, David J.
This report describes the stratified adaptive (stradaptive) test as a strategy for tailoring an ability test to individual differences in testee ability; administration of the test is controlled by a time-shared computer system. The rationale of this method is described as it derives from Binet's strategy of ability test administration and…
Mixing efficiency of turbulent stratified flows
NASA Astrophysics Data System (ADS)
White, B. L.; Scotti, A. D.
2012-12-01
Small-scale mixing in the stratified interior of the ocean is a fundamental, but poorly characterized, controlling factor of the global Meridional Overturning Circulation (MOC). The mixing efficiency in the ocean has typically been assumed to be 20%, which is used as a basis to estimate the required turbulent dissipation to support the ocean diapycnal buoyancy flux. In this talk, we use DNS datasets to calculate the mixing efficiency in different classes of stratified turbulent flows. In particular, we compare flows forced thermodynamically by production of Available Potential Energy (APE) at a boundary, such as horizontal convection (a simple model for an ocean forced by differential surface heating) and flows that are forced mechanically by surface stresses. The mixing efficiency is calculated based on the irreversible diapycnal flux of buoyancy (Winters and D'Asaro, 1996; Scotti et al., 2006) instead of the more customary turbulent buoyancy flux, thereby isolating mixing from reversible processes (e.g., internal waves). For mechanically-driven flows, profiles of mixing efficiency vs. buoyancy Reynolds number are in agreement with accepted values for stratified turbulent shear flows. However, for flows in which mixing is driven in part or fully by thermodynamic forcing and an excess of APE, DNS results show much higher values of the mixing efficiency, approaching unity for horizontal convection. Implications of these results for the energy budget of the MOC are discussed. Note: The DNS data sets of turbulent stratified channel flow are provided courtesy of M. Garcia-Villalba and J. C. del Alamo.
Hassan, T.A.
1992-12-01
The practical use of Pulsed Laser Velocimetry (PLV) requires the use of fast, reliable computer-based methods for tracking numerous particles suspended in a fluid flow. Two methods for performing tracking are presented. One method tracks a particle through multiple sequential images (minimum of four required) by prediction and verification of particle displacement and direction. The other method, requiring only two sequential images uses a dynamic, binary, spatial, cross-correlation technique. The algorithms are tested on computer-generated synthetic data and experimental data which was obtained with traditional PLV methods. This allowed error analysis and testing of the algorithms on real engineering flows. A novel method is proposed which eliminates tedious, undersirable, manual, operator assistance in removing erroneous vectors. This method uses an iterative process involving an interpolated field produced from the most reliable vectors. Methods are developed to allow fast analysis and presentation of sets of PLV image data. Experimental investigation of a two-phase, horizontal, stratified, flow regime was performed to determine the interface drag force, and correspondingly, the drag coefficient. A horizontal, stratified flow test facility using water and air was constructed to allow interface shear measurements with PLV techniques. The experimentally obtained local drag measurements were compared with theoretical results given by conventional interfacial drag theory. Close agreement was shown when local conditions near the interface were similar to space-averaged conditions. However, theory based on macroscopic, space-averaged flow behavior was shown to give incorrect results if the local gas velocity near the interface as unstable, transient, and dissimilar from the average gas velocity through the test facility.
NASA Technical Reports Server (NTRS)
Chiaramonte, Francis; Motil, Brian; McQuillen, John
2014-01-01
The Two-phase Heat Transfer International Topical Team consists of researchers and members from various space agencies including ESA, JAXA, CSA, and RSA. This presentation included descriptions various fluid experiments either being conducted by or planned by NASA for the International Space Station in the areas of two-phase flow, flow boiling, capillary flow, and crygenic fluid storage.
48 CFR 570.305 - Two-phase design-build selection procedures.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 48 Federal Acquisition Regulations System 4 2011-10-01 2011-10-01 false Two-phase design-build...-phase design-build selection procedures. (a) These procedures apply to acquisitions of leasehold interests if the contracting officer uses the two-phase design-build selection procedures authorized by...
Majhi, Bijoy Kumar; Jash, Tushar
2016-12-01
Biogas production from vegetable market waste (VMW) fraction of municipal solid waste (MSW) by two-phase anaerobic digestion system should be preferred over the single-stage reactors. This is because VMW undergoes rapid acidification leading to accumulation of volatile fatty acids and consequent low pH resulting in frequent failure of digesters. The weakest part in the two-phase anaerobic reactors was the techniques applied for solid-liquid phase separation of digestate in the first reactor where solubilization, hydrolysis and acidogenesis of solid organic waste occur. In this study, a two-phase reactor which consisted of a solid-phase reactor and a methane reactor was designed, built and operated with VMW fraction of Indian MSW. A robust type filter, which is unique in its implementation method, was developed and incorporated in the solid-phase reactor to separate the process liquid produced in the first reactor. Experiments were carried out to assess the long term performance of the two-phase reactor with respect to biogas production, volatile solids reduction, pH and number of occurrence of clogging in the filtering system or choking in the process liquid transfer line. The system performed well and was operated successfully without the occurrence of clogging or any other disruptions throughout. Biogas production of 0.86-0.889m(3)kg(-1)VS, at OLR of 1.11-1.585kgm(-3)d(-1), were obtained from vegetable market waste, which were higher than the results reported for similar substrates digested in two-phase reactors. The VS reduction was 82-86%. The two-phase anaerobic digestion system was demonstrated to be stable and suitable for the treatment of VMW fraction of MSW for energy generation.
A two phase Mach number description of the equilibrium flow of nitrogen in ducts
NASA Technical Reports Server (NTRS)
Bursik, J. W.; Hall, R. M.; Adcock, J. B.
1979-01-01
Some additional thermodynamic properties of the usual two-phase form which is linear in the moisture fraction are derived which are useful in the analysis of many kinds of duct flow. The method used is based on knowledge of the vapor pressure and Gibbs function as functions of temperature. With these, additional two-phase functions linear in moisture fraction are generated, which ultimately reveal that the squared ratio of mixture specific volume to mixture sound speed depends on liquid mass fraction and temperature in the same manner as do many weighted mean two-phase properties. This leads to a simple method of calculating two-phase Mach numbers for various duct flows. The matching of one- and two-phase flows at a saturated vapor point with discontinuous Mach number is also discussed.
On-demand generation of aqueous two-phase microdroplets with reversible phase transitions
Boreyko, Jonathan B; Mruetusatorn, Prachya; Retterer, Scott T; Collier, Pat
2013-01-01
Aqueous two-phase systems contained entirely within microdroplets enable a bottom-up approach to mimicking the dynamic microcompartmentation of biomaterial that naturally occurs within the cytoplasm of cells. Here, we demonstrate the on-demand generation of femtolitre aqueous two-phase droplets within a microfluidic oil channel. Gated pressure pulses were used to generate individual, stationary two-phase microdroplets with a well-defined time zero for carrying out controlled and sequential phase transformations over time. Reversible phase transitions between single-phase, two-phase, and core-shell microgel states were obtained via evaporation-induced dehydration and on-demand water rehydration. In contrast to other microfluidic aqueous two-phase droplets, which require continuous flows and high-frequency droplet formation, our system enables the controlled isolation and reversible transformation of a single microdroplet and is expected to be useful for future studies in dynamic microcompartmentation and affinity partitioning.
Settling and swimming in density stratified fluids
NASA Astrophysics Data System (ADS)
Ardekani, Arezoo
2016-11-01
Many aquatic environments are stratified, characterized by regions of vertical variation in fluid density caused by gradients in temperature or salinity. In oceans and lakes, intense biological activity and accumulation of particles and organisms are associated with pycnoclines and the occurrence of important environmental and oceanographic processes is correlated with stratification. We explore the effects of stratification on the fundamental hydrodynamics of small organisms, settling particles, and rising drops. These results demonstrate an unexpected effect of buoyancy, potentially affecting a broad range of processes at pycnoclines in oceans and lakes. In particular, stratification has a major effect on the flow field, energy expenditure and nutrient uptake of small organisms. We show that elongation affects both the settling orientation and the settling rate of particles in stratified fluids, which will have direct consequences on the vertical flux of particulate matter and carbon flux in the ocean.
Multiscale equations for strongly stratified turbulent flows
NASA Astrophysics Data System (ADS)
Chini, Greg; Rocha, Cesar; Julien, Keith; Caulfield, Colm-Cille
2016-11-01
Strongly stratified turbulent shear flows are of fundamental importance owing to their widespread occurrence and their impact on diabatic mixing, yet direct numerical simulations of such flows remain challenging. Here, a reduced, multiscale description of turbulent shear flows in the presence of strong stable density stratification is derived via asymptotic analysis of the governing Boussinesq equations. The analysis explicitly recognizes the occurrence of dynamics on disparate spatiotemoporal scales, and yields simplified partial differential equations governing the coupled evolution of slowly-evolving small aspect-ratio ('pancake') modes and isotropic, strongly non-hydrostatic stratified-shear (e.g. Kelvin-Helmholtz) instability modes. The reduced model is formally valid in the physically-relevant regime in which the aspect-ratio of the pancake structures tends to zero in direct proportion to the horizontal Froude number. Relative to the full Boussinesq equations, the model offers both computational and conceptual advantages.
Low Mach Number Modeling of Stratified Flows
NASA Astrophysics Data System (ADS)
Almgren, A. S.; Bell, J. B.; Nonaka, A.; Zingale, M.
2015-06-01
Low Mach number equation sets approximate the equations of motion of a compressible fluid by filtering out the sound waves, which allows the system to evolve on the advective rather than the acoustic time scale. Depending on the degree of approximation, low Mach number models retain some sub set of possible compressible effects. In this paper we give an overview of low Mach number methods for modeling stratified flows arising in astrophysics and atmospheric science as well as low Mach number reacting flows. We discuss how elements from the different fields are combined to form MAESTRO, a code for modeling low Mach number stratified flows with general equations of state, reactions and time-varying stratification.
Nitrogen transformations in stratified aquatic microbial ecosystems.
Revsbech, Niels Peter; Risgaard-Petersen, Nils; Schramm, Andreas; Nielsen, Lars Peter
2006-11-01
New analytical methods such as advanced molecular techniques and microsensors have resulted in new insights about how nitrogen transformations in stratified microbial systems such as sediments and biofilms are regulated at a microm-mm scale. A large and ever-expanding knowledge base about nitrogen fixation, nitrification, denitrification, and dissimilatory reduction of nitrate to ammonium, and about the microorganisms performing the processes, has been produced by use of these techniques. During the last decade the discovery of anammmox bacteria and migrating, nitrate accumulating bacteria performing dissimilatory reduction of nitrate to ammonium have given new dimensions to the understanding of nitrogen cycling in nature, and the occurrence of these organisms and processes in stratified microbial communities will be described in detail.
Stably Stratified Flow in a Shallow Valley
NASA Astrophysics Data System (ADS)
Mahrt, L.
2017-01-01
Stratified nocturnal flow above and within a small valley of approximately 12-m depth and a few hundred metres width is examined as a case study, based on a network of 20 sonic anemometers and a central 20-m tower with eight levels of sonic anemometers. Several regimes of stratified flow over gentle topography are conceptually defined for organizing the data analysis and comparing with the existing literature. In our case study, a marginal cold pool forms within the shallow valley in the early evening but yields to larger ambient wind speeds after a few hours, corresponding to stratified terrain-following flow where the flow outside the valley descends to the valley floor. The terrain-following flow lasts about 10 h and then undergoes transition to an intermittent marginal cold pool towards the end of the night when the larger-scale flow collapses. During this 10-h period, the stratified terrain-following flow is characterized by a three-layer structure, consisting of a thin surface boundary layer of a few metres depth on the valley floor, a deeper boundary layer corresponding to the larger-scale flow, and an intermediate transition layer with significant wind-directional shear and possible advection of lee turbulence that is generated even for the gentle topography of our study. The flow in the valley is often modulated by oscillations with a typical period of 10 min. Cold events with smaller turbulent intensity and duration of tens of minutes move through the observational domain throughout the terrain-following period. One of these events is examined in detail.
NASA Astrophysics Data System (ADS)
Gurung, Arati; Poelma, Christian
2016-11-01
Ultrasound imaging velocimetry (UIV) has received considerable interest as a tool to measure in non-transparent flows. So far, studies have only reported statistics for steady flows or used a qualitative approach. In this study, we demonstrate that UIV has matured to a level where accurate turbulence statistics can be obtained. The technique is first validated in laminar and fully developed turbulent pipe flow (single-phase, with water as fluid) at a Reynolds number of 5300. The flow statistics agree with the literature data. Subsequently, we obtain similar statistics in turbulent two-phase flows at the same Reynolds number, by adding solid particles up to volume fraction of 3 %. In these cases, the medium is completely opaque, yet UIV provides useable data. The error in the measurements is estimated using an ad hoc approach at a volume load up to 10 %. For this case, the errors are approximately 1.9 and 0.3 % of the centerline velocity for the streamwise and radial velocity components, respectively. Additionally, it is demonstrated that it is possible to estimate the local concentration in stratified flows.
Thermal mixing in a stratified environment
NASA Astrophysics Data System (ADS)
Kraemer, Damian; Cotel, Aline
1999-11-01
Laboratory experiments of a thermal impinging on a stratified interface have been performed. The thermal was released from a cylindrical reservoir located at the bottom of a Lucite tank. The stratified interface was created by filling the tank with two different saline solutions. The density of the lower layer is greater than that of the upper layer and the thermal fluid, thereby creating a stable stratification. A pH indicator, phenolphthalein, is used to visualize and quantify the amount of mixing produced by the impingement of the thermal at the interface. The upper layer contains a mixture of water, salt and sodium hydroxide. The thermal fluid is composed of water, sulfuric acid and phenolphthalein. When the thermal entrains and mixes fluid from the upper layer, a chemical reaction takes place, and the resulting mixed fluid is now visible. The ratio of base to acid, called the equivalence ratio, was varied throughout the experiments, as well as the Richardson number. The Richardson number is the ratio of potential to kinetic energy, and is based on the thermal quantities at the interface. Results indicate that the amount of mixing produced is proportional to the Richardson number raised to the -3/2 power. Previous experiments (Zhang and Cotel 1999) revealed that the entrainment rate of a thermal in a stratified environment follows the same power law.
Evolution of a forced stratified mixing layer
NASA Astrophysics Data System (ADS)
Rotter, J.; Fernando, H. J. S.; Kit, E.
2007-06-01
Laboratory measurements were carried out in a spatially developing stably stratified shear layer generated downstream of a splitter plate. The instabilities were controlled using a flapper spanning the entire shear layer, with the flapper forced at the fastest growing frequency of the primary [Kelvin-Helmholtz (KH)] instability. The measurements were taken as the KH instabilities roll up, break down, and degenerate into stratified turbulence. Both stratified and homogeneous shear layers were considered, the latter acting as the "baseline" case. The measurements included the streamwise and vertical velocities (made using X-wire hot film probes), which allowed calculation of the mean and rms velocities, turbulent kinetic energy (TKE) dissipation, and TKE production. The density and its gradients were measured using miniature conductivity probes. The measurements and flow visualization elicited interesting features of KH evolution, namely that KH billows may be turbulent from the onset, the TKE dissipation is largest at early stages of evolution, the production of TKE is a maximum at the breakdown of billows, the decay of turbulence to fossilized motions and concomitant formation of fine (layered) structure occur rapidly after the breakdown of billows, and episodic rebirth of (zombie) turbulence develops before a final permanently fossilized state is achieved.
The measurement of thermodynamic performance in cryogenic two-phase turbo-expander
NASA Astrophysics Data System (ADS)
Niu, Lu; Hou, Yu; Sun, Wan; Chen, Shuangtao
2015-09-01
Liquid fraction measurement in cryogenic two-phase flow is a complex issue, especially for an industrial cryogenic system. In this paper, a simple thermal method is proposed for measuring the liquid fraction in cryogenic two-phase turbo-expander by an electric heating unit in experimental study. The liquid fraction of the cryogenic two-phase flow is determined through the heat balance built at the outlet of the turbo-expander (inlet of heating unit) and the outlet of the heating unit. Liquid fractions from 1.16% to 5.02% are obtained from five two-phase expansion cases. Under the same turbo-expander inlet pressure and rotating speed, five superheated expansion cases are tested to evaluate the wetness loss in two-phase expansion. The results show that the proposed method is successful in measuring the liquid fraction of cryogenic two-phase expansion for turbo-expander in an industrial air separation plant. The experimental isentropic efficiency ratio and the tested Baumann factor decrease with the increasing mean wetness. Based on prediction of Baumann rule, the cryogenic turbo-expander with low liquid fraction in two-phase expansion cases suffers from more severe wetness loss than that with the higher liquid fraction.
Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells
NASA Astrophysics Data System (ADS)
Wang, Z. H.; Wang, C. Y.; Chen, K. S.
Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Single- and two-phase regimes of water distribution and transport are classified by a threshold current density corresponding to first appearance of liquid water at the membrane/cathode interface. When the cell operates above the threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multicomponent mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone of the hydrophilic structure. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A cm -2 for dry inlet air.
Single and two-phase flow fluid dynamics in parallel helical coils
NASA Astrophysics Data System (ADS)
De Salve, M.; Orio, M.; Panella, B.
2014-04-01
The design of helical coiled steam generators requires the knowledge of the single and two-phase fluid dynamics. The present work reports the results of an experimental campaign on single-phase and two phase pressure drops and void fraction in three parallel helicoidal pipes, in which the total water flow rate is splitted by means of a branch. With this test configuration the distribution of the water flow rate in the helicoidal pipes and the phenomena of the instability of the two-phase flow have been experimentally investigated.
Thermophysics of two-phase flows in microgravity: Russian-American research project
NASA Astrophysics Data System (ADS)
Leontiev, A. I.; Diev, M. D.; Cykhotsky, V. M.; Prokhorov, Y. M.; Bednov, S. M.; Desyatov, A. V.; Blinkov, V. N.; Gorbenko, G. A.; Kopyatkevich, R. M.
1997-01-01
Thermal control systems of space vehicles, being developed and prospective, including heavy weight orbital stations, platforms, interplanetary missions, lunar villages and modules, will be most likely based on two-phase heat transport loops. The paper presents complex program of fundamental and applied studies of two-phase hydrodynamics and heat transfer in microgravity. The program is being performed by four Russian organizations under financial support by NASA. It is directed towards solution of practical problems arising when International Space Station ALPHA Russian Segment (ISSA RS) Two-Phase Thermal Control System (TPS) is being designed.
Experimental study of flow oscillations in parallel evaporators of a carbon dioxide two-phase loop
NASA Astrophysics Data System (ADS)
Sun, Xihui; He, Zhenhui; Huang, Zhencheng
2013-07-01
Stability is a key factor that limits the application of liquid-vapor two-phase loop. in this paper, we investigated the two-phase flow stability boundaries of two evaporators in parallel in a mechanically pumped CO2 two-phase loop(MPTL), which distinguish steady flow, flow oscillations at the inlet, and temperature oscillations at the outlets of the evaporators. We inferred that the instability is the result of density wave oscillation (DWO), and found that the periods of the flow oscillations are comparable with the residence time of CO2 fluid particle in the evaporator.
Reduced gravity and ground testing of a two-phase thermal management system for large spacecraft
NASA Technical Reports Server (NTRS)
Hill, D. G.; Hsu, K.; Parish, R.; Dominick, J.
1988-01-01
Experiments were performed aboard the NASA-JSC KC-135 aircraft to study the effect of reduced gravity on two-phase (liquid/vapor) flow and condensation. A prototype two-phase thermal management system for a large spacecraft was tested. Both visual observation and photography of the flow regimes were made. Ground test simulations of the KC-135 flight tests were conducted for comparison purposes. Two-phase pressure drops were predictable by the Heat Transfer Research Institute (HTRI) method, or the Friedel correlation.
Roberge, Cornelia; Wulff, Sören; Reese, Heather; Ståhl, Göran
2016-04-01
Many countries have a national forest inventory (NFI) designed to produce statistically sound estimates of forest parameters. However, this type of inventory may not provide reliable results for forest damage which usually affects only small parts of the forest in a country. For this reason, specially designed forest damage inventories are performed in many countries, sometimes in coordination with the NFIs. In this study, we evaluated a new approach for damage inventory where existing NFI data form the basis for two-phase sampling for stratification and remotely sensed auxiliary data are applied for further improvement of precision through post-stratification. We applied Monte Carlo sampling simulation to evaluate different sampling strategies linked to different damage scenarios. The use of existing NFI data in a two-phase sampling for stratification design resulted in a relative efficiency of 50 % or lower, i.e., the variance was at least halved compared to a simple random sample of the same size. With post-stratification based on simulated remotely sensed auxiliary data, there was additional improvement, which depended on the accuracy of the auxiliary data and the properties of the forest damage. In many cases, the relative efficiency was further reduced by as much as one-half. In conclusion, the results show that substantial gains in precision can be obtained by utilizing auxiliary information in forest damage surveys, through two-phase sampling, through post-stratification, and through the combination of these two approaches, i.e., post-stratified two-phase sampling for stratification.
Li, Jiao Jiao; Kim, Kyungsook; Roohani-Esfahani, Seyed-Iman; Guo, Jin; Kaplan, David L; Zreiqat, Hala
2015-07-14
Significant clinical challenges encountered in the effective long-term treatment of osteochondral defects have inspired advancements in scaffold-based tissue engineering techniques to aid repair and regeneration. This study reports the development of a biphasic scaffold produced via a rational combination of silk fibroin and bioactive ceramic with stratified properties to satisfy the complex and diverse regenerative requirements of osteochondral tissue. Structural examination showed that the biphasic scaffold contained two phases with different pore morphologies to match the cartilage and bone segments of osteochondral tissue, which were joined at a continuous interface. Mechanical assessment showed that the two phases of the biphasic scaffold imitated the load-bearing behaviour of native osteochondral tissue and matched its compressive properties. In vitro testing showed that different compositions in the two phases of the biphasic scaffold could direct the preferential differentiation of human mesenchymal stem cells towards the chondrogenic or osteogenic lineage. By featuring simple and reproducible fabrication and a well-integrated interface, the biphasic scaffold strategy established in this study circumvented the common problems experienced with integrated scaffold designs and could provide an effective approach for the regeneration of osteochondral tissue.
A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries
Dong, S.; Wang, X.
2016-01-01
Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries. PMID:27163909
Future directions in two-phase flow and heat transfer in space
NASA Technical Reports Server (NTRS)
Bankoff, S. George
1994-01-01
Some areas of opportunity for future research in microgravity two-phase flow and heat transfer are pointed out. These satisfy the dual requirements of relevance to current and future needs, and scientific/engineering interest.
A theoretical evaluation of aluminum gel propellant two-phase flow losses on vehicle performance
NASA Technical Reports Server (NTRS)
Mueller, Donn C.; Turns, Stephen R.
1993-01-01
A one-dimensional model of a hydrocarbon/Al/O2(gaseous) fueled rocket combustion chamber was developed to study secondary atomization effects on propellant combustion. This chamber model was coupled with a two dimensional, two-phase flow nozzle code to estimate the two-phase flow losses associated with solid combustion products. Results indicate that moderate secondary atomization significantly reduces propellant burnout distance and Al2O3 particle size; however, secondary atomization provides only moderate decreases in two-phase flow induced I(sub sp) losses. Despite these two-phase flow losses, a simple mission study indicates that aluminum gel propellants may permit a greater maximum payload than the hydrocarbon/O2 bi-propellant combination for a vehicle of fixed propellant volume. Secondary atomization was also found to reduce radiation losses from the solid combustion products to the chamber walls, primarily through reductions in propellant burnout distance.
Two-phase turbine engines. [using gas-liquid mixture accelerated in nozzles
NASA Technical Reports Server (NTRS)
Elliott, D. G.; Hays, L. G.
1976-01-01
A description is given of a two-phase turbine which utilizes a uniform mixture of gas and liquid accelerated in nozzles of the types reported by Elliott and Weinberg (1968). The mixture acts directly on an axial flow or tangential impulse turbine or is separated into gas and liquid streams which operate separately on a gas turbine and a hydraulic turbine. The basic two-phase cycles are examined, taking into account working fluids, aspects of nozzle expansion, details of turbine cycle operation, and the effect of mixture ratio variation. Attention is also given to two-phase nozzle efficiency, two-phase turbine operating characteristics and efficiencies, separator turbines, and impulse turbine experiments.
Development of an Enhanced Two-Phase Production System at the Geysers Geothermal Field
Steven Enedy
2001-12-14
A method was developed to enhance geothermal steam production from two-phase wells at THE Geysers Geothermal Field. The beneficial result was increased geothermal production that was easily and economically delivered to the power plant.
Experimental and Analytical Study of Two-Phase Flow in Microgravity
NASA Technical Reports Server (NTRS)
Abdollahian, D.; Howerton, J.; Barez, F.; McQuillen, John
1999-01-01
A two-phase test loop has been designed and constructed to generate the necessary data for two-phase pressure drop and Critical Heat Flux (CHF) under reduced gravity conditions. A series of airplane trajectory tests aboard NASA KC-135 were performed and the data was used to evaluate the applicability of the earth gravity models for prediction of the reduced gravity data. Several commonly used correlations for the two-phase friction multiplier and critical heat flux were used to predict the data. It was generally concluded that the two-phase pressure drop can be predicted by the earth gravity correlations. The critical heat flux under reduced gravity conditions did not show a strong dependence on mass flow rate and the measured CHF were generally lower than the equivalent 1g conditions. The earth gravity models need to be modified for application to reduced gravities.
Study of two-phase flow and heat transfer in reduced gravities
NASA Technical Reports Server (NTRS)
Abdollahian, Davood; Barez, Fred
1994-01-01
Design of the two-phase systems which are anticipated to be utilized in future spacecraft thermal management systems requires a knowledge of two-phase flow and heat transfer parameters in reduced gravities. A program has been initiated by NASA to design a two-phase test loop and perform a series of experiments to generate the data for the Critical Heat Flux (CHF) and onset of instability under reduced gravities. In addition to low gravity airplane trajectory testing, the experimental program consists of a set of laboratory tests with vertical upflow and downflow configurations. Modularity is considered in the design of this experiment and the test loop in instrumented to provide data for two-phase pressure drop and flow regime behavior. Since the program is in the final stages of the design and construction task, this article is intended to discuss the phenomena, design approach, and the description of the test loop.
Irreversible entropy production in two-phase flows with evaporating drops
NASA Technical Reports Server (NTRS)
Bellan, J.; Okong'o, N. A.
2002-01-01
A derivation of the irreversible entropy production, that is the dissipation, in two-phase flows is presented for the purpose of examining the effect of evaporative-drop modulation of flows having turbulent features.
Numerical simulation of multi-dimensional two-phase flow based on flux vector splitting
Staedtke, H.; Franchello, G.; Worth, B.
1995-09-01
This paper describes a new approach to the numerical simulation of transient, multidimensional two-phase flow. The development is based on a fully hyperbolic two-fluid model of two-phase flow using separated conservation equations for the two phases. Features of the new model include the existence of real eigenvalues, and a complete set of independent eigenvectors which can be expressed algebraically in terms of the major dependent flow parameters. This facilitates the application of numerical techniques specifically developed for high speed single-phase gas flows which combine signal propagation along characteristic lines with the conservation property with respect to mass, momentum and energy. Advantages of the new model for the numerical simulation of one- and two- dimensional two-phase flow are discussed.
A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries.
Dong, S; Wang, X
2016-01-01
Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries.
Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary
2014-06-10
A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.
Turbulence production in stratified Ekman flow
NASA Astrophysics Data System (ADS)
Mkhinini, Nadia; Dubos, Thomas; Drobinski, Philippe
2010-05-01
Although a stable stratification should suppress vertical motions and turbulence, significant turbulence is observed in nocturnal or polar atmospheric boundary layers (ABLs), and often presents a high degree of instationarity or intermittency. In this work we use the Ekman flow as a prototype flow to explore possible dynamical mechanisms generating this turbulence. The linear instability of neutral and stratified Ekman flow has been studied theoretically and experimentally (Lilly, 1966 ; Brown, 1972). The fastest growing infinitesimal perturbations equilibrate nonlinearly in the form of longitudinal roll vortices which are close analogues of circulations found in neutral and weakly convective ABLs (Brown, 1970 ; Young, 2002). Therefore a secondary instability mechanism must be invoked for three-dimensional (3D) turbulence to be generated. Through such a mechanism, which is known to exist in the neutral case (Dubos et al., 2008), infinitesimal 3D perturbations to the equilibrated rolls grow and eventually lead to turbulence through nonlinear interactions. Vortices and stratified shear flows present various types of secondary instability (Godeferd et al., 2001 ; Peltier and Caulfield, 2003). We perform the secondary stability analysis of stratified Ekman boundary layer rolls for a few values of the Reynolds, Richardson and Prandtl numbers. For this, we first compute the equilibrated rolls and discuss their structure. Especially their exists a range of intermediate Richardson numbers for which locally unstable stratification is present in the vortex core. This feature provides a potential mechanism and energy source for the secondary instability. The energetics of the growth of three-dimensional perturbations are discussed for a few representative values of the control parameters.
The fully nonlinear stratified geostrophic adjustment problem
NASA Astrophysics Data System (ADS)
Coutino, Aaron; Stastna, Marek
2017-01-01
The study of the adjustment to equilibrium by a stratified fluid in a rotating reference frame is a classical problem in geophysical fluid dynamics. We consider the fully nonlinear, stratified adjustment problem from a numerical point of view. We present results of smoothed dam break simulations based on experiments in the published literature, with a focus on both the wave trains that propagate away from the nascent geostrophic state and the geostrophic state itself. We demonstrate that for Rossby numbers in excess of roughly 2 the wave train cannot be interpreted in terms of linear theory. This wave train consists of a leading solitary-like packet and a trailing tail of dispersive waves. However, it is found that the leading wave packet never completely separates from the trailing tail. Somewhat surprisingly, the inertial oscillations associated with the geostrophic state exhibit evidence of nonlinearity even when the Rossby number falls below 1. We vary the width of the initial disturbance and the rotation rate so as to keep the Rossby number fixed, and find that while the qualitative response remains consistent, the Froude number varies, and these variations are manifested in the form of the emanating wave train. For wider initial disturbances we find clear evidence of a wave train that initially propagates toward the near wall, reflects, and propagates away from the geostrophic state behind the leading wave train. We compare kinetic energy inside and outside of the geostrophic state, finding that for long times a Rossby number of around one-quarter yields an equal split between the two, with lower (higher) Rossby numbers yielding more energy in the geostrophic state (wave train). Finally we compare the energetics of the geostrophic state as the Rossby number varies, finding long-lived inertial oscillations in the majority of the cases and a general agreement with the past literature that employed either hydrostatic, shallow-water equation-based theory or
NASA Astrophysics Data System (ADS)
Musa Abbagoni, Baba; Yeung, Hoi
2016-08-01
The identification of flow pattern is a key issue in multiphase flow which is encountered in the petrochemical industry. It is difficult to identify the gas-liquid flow regimes objectively with the gas-liquid two-phase flow. This paper presents the feasibility of a clamp-on instrument for an objective flow regime classification of two-phase flow using an ultrasonic Doppler sensor and an artificial neural network, which records and processes the ultrasonic signals reflected from the two-phase flow. Experimental data is obtained on a horizontal test rig with a total pipe length of 21 m and 5.08 cm internal diameter carrying air-water two-phase flow under slug, elongated bubble, stratified-wavy and, stratified flow regimes. Multilayer perceptron neural networks (MLPNNs) are used to develop the classification model. The classifier requires features as an input which is representative of the signals. Ultrasound signal features are extracted by applying both power spectral density (PSD) and discrete wavelet transform (DWT) methods to the flow signals. A classification scheme of ‘1-of-C coding method for classification’ was adopted to classify features extracted into one of four flow regime categories. To improve the performance of the flow regime classifier network, a second level neural network was incorporated by using the output of a first level networks feature as an input feature. The addition of the two network models provided a combined neural network model which has achieved a higher accuracy than single neural network models. Classification accuracies are evaluated in the form of both the PSD and DWT features. The success rates of the two models are: (1) using PSD features, the classifier missed 3 datasets out of 24 test datasets of the classification and scored 87.5% accuracy; (2) with the DWT features, the network misclassified only one data point and it was able to classify the flow patterns up to 95.8% accuracy. This approach has demonstrated the
Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code
Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.
1992-01-01
FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime.
Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code
Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.
1992-12-31
FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime.
Estimation of the sugar cane cultivated area from LANDSAT images using the two phase sampling method
NASA Technical Reports Server (NTRS)
Parada, N. D. J. (Principal Investigator); Cappelletti, C. A.; Mendonca, F. J.; Lee, D. C. L.; Shimabukuro, Y. E.
1982-01-01
A two phase sampling method and the optimal sampling segment dimensions for the estimation of sugar cane cultivated area were developed. This technique employs visual interpretations of LANDSAT images and panchromatic aerial photographs considered as the ground truth. The estimates, as a mean value of 100 simulated samples, represent 99.3% of the true value with a CV of approximately 1%; the relative efficiency of the two phase design was 157% when compared with a one phase aerial photographs sample.
Three-phase-to-two-phase direct AC-AC converter with three leg structure
NASA Astrophysics Data System (ADS)
Kwak, S.-S.
2014-05-01
A three-phase-to-two-phase ac-ac converter is, along with a modulation strategy based on the space vector scheme, introduced to directly drive two-phase output ac systems with high input power quality. The converter is capable of synthesising two sinusoidal output voltages with variable output frequency and arbitrary magnitude in quadrature phase-shift as well as sinusoidal input currents.
White dwarf stars with chemically stratified atmospheres
NASA Technical Reports Server (NTRS)
Muchmore, D.
1982-01-01
Recent observations and theory suggest that some white dwarfs may have chemically stratified atmospheres - thin layers of hydrogen lying above helium-rich envelopes. Models of such atmospheres show that a discontinuous temperature inversion can occur at the boundary between the layers. Model spectra for layered atmospheres at 30,000 K and 50,000 K tend to have smaller decrements at 912 A, 504 A, and 228 A than uniform atmospheres would have. On the basis of their continuous extreme ultraviolet spectra, it is possible to distinguish observationally between uniform and layered atmospheres for hot white dwarfs.
Topological Structures in Rotating Stratified Flows
NASA Astrophysics Data System (ADS)
Redondo, J. M.; Carrillo, A.; Perez, E.
2003-04-01
Detailled 2D Particle traking and PIV visualizations performed on a series of large scale laboratory experiments at the Coriolis Platform of the SINTEF in Trondheim have revealed several resonances which scale on the Strouhal, the Rossby and the Richardson numbers. More than 100 experiments spanned a wide range of Rossby Deformation Radii and the topological structures (Parabolic /Eliptic /Hyperbolic) of the quasi-balanced stratified-rotating flows were studied when stirring (akin to coastal mixing) occured at a side of the tank. The strong asymetry favored by the total vorticity produces a wealth of mixing patterns.
A Filtering Method For Gravitationally Stratified Flows
Gatti-Bono, Caroline; Colella, Phillip
2005-04-25
Gravity waves arise in gravitationally stratified compressible flows at low Mach and Froude numbers. These waves can have a negligible influence on the overall dynamics of the fluid but, for numerical methods where the acoustic waves are treated implicitly, they impose a significant restriction on the time step. A way to alleviate this restriction is to filter out the modes corresponding to the fastest gravity waves so that a larger time step can be used. This paper presents a filtering strategy of the fully compressible equations based on normal mode analysis that is used throughout the simulation to compute the fast dynamics and that is able to damp only fast gravity modes.
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe
2011-01-01
A two-phase flow experiment using air and water-based γ-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fraction distribution was flattened in the nanofluid case more than it was in the pure water case. The higher interfacial area concentration resulted in a smaller mean bubble diameter in the case of the nanofluid. This was the first attempt to measure the local two-phase flow parameters of nanofluids using a conductivity double-sensor two-phase void meter. Throughout this experimental study, the differences in the internal two-phase flow structure of the nanofluid were identified. In addition, the heat transfer enhancement of the nanofluid can be resulted from the increase of the interfacial area concentration which means the available area of the heat and mass transfer. PMID:21711823
A study of two-phase flow in a reduced gravity environment
NASA Technical Reports Server (NTRS)
Hill, D.; Downing, Robert S.
1987-01-01
A test loop was designed and fabricated for observing and measuring pressure drops of two-phase flow in reduced gravity. The portable flow test loop was then tested aboard the NASA-JSC KC135 reduced gravity aircraft. The test loop employed the Sundstrand Two-Phase Thermal Management System (TPTMS) concept which was specially fitted with a clear two-phase return line and condenser cover for flow observation. A two-phase (liquid/vapor) mixture was produced by pumping nearly saturated liquid through an evaporator and adding heat via electric heaters. The quality of the two-phase flow was varied by changing the evaporator heat load. The test loop was operated on the ground before and after the KC135 flight tests to create a one-gravity data base. The ground testing included all the test points run during the reduced gravity testing. Two days of reduced gravity tests aboard the KC135 were performed. During the flight tests, reduced-gravity, one-gravity, and nearly two-gravity accelerations were experienced. Data was taken during the entire flight which provided flow regime and pressure drop data for the three operating conditions. The test results show that two-phase pressure drops and flow regimes can be accurately predicted in zero-gravity.
Oppermann, Sebastian; Stein, Florian; Kragl, Udo
2011-02-01
The development of biotechnological processes using novel two-phase systems based on molten salts known as ionic liquids (ILs) got into the focus of interest. Many new approaches for the beneficial application of the interesting solvent have been published over the last years. ILs bring beneficial properties compared to organic solvents like nonflammability and nonvolatility. There are two possible ways to use the ILs: first, the hydrophobic ones as a substitute for organic solvents in pure two-phase systems with water and second, the hydrophilic ones in aqueous two-phase systems (ATPS). To effectively utilise IL-based two-phase systems or IL-based ATPS in biotechnology, extensive experimental work is required to gain the optimal system parameters to ensure selective extraction of the product of interest. This review will focus on the most actual findings dealing with the basic driving forces for the target extraction in IL-based ATPS as well as presenting some selected examples for the beneficial application of ILs as a substitute for organic solvents. Besides the research focusing on IL-based two-phase systems, the "green aspect" of ILs, due to their negligible vapour pressure, is widely discussed. We will present the newest results concerning ecotoxicity of ILs to get an overview of the state of the art concerning ILs and their utilisation in novel two-phase systems in biotechnology.
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe.
Park, Yu Sun; Chang, Soon Heung
2011-04-04
A two-phase flow experiment using air and water-based γ-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fraction distribution was flattened in the nanofluid case more than it was in the pure water case. The higher interfacial area concentration resulted in a smaller mean bubble diameter in the case of the nanofluid. This was the first attempt to measure the local two-phase flow parameters of nanofluids using a conductivity double-sensor two-phase void meter. Throughout this experimental study, the differences in the internal two-phase flow structure of the nanofluid were identified. In addition, the heat transfer enhancement of the nanofluid can be resulted from the increase of the interfacial area concentration which means the available area of the heat and mass transfer.
Living between two worlds: two-phase culture systems for producing plant secondary metabolites.
Malik, Sonia; Hossein Mirjalili, Mohammad; Fett-Neto, Arthur Germano; Mazzafera, Paulo; Bonfill, Mercedes
2013-03-01
The two-phase culture system is an important in vitro strategy to increase the production of secondary metabolites (SMs) by providing an enhanced release of these compounds from plant cells. Whereas the first phase supports cell growth, the second phase provides an additional site or acts as a metabolic sink for the accumulation of SMs and also reduces feedback inhibition. This review is focused on several aspects of the two-phase culture system and aims to show the diverse possibilities of employing this technique for the in vitro production of SMs from plant cells. Depending on the material used in the secondary phase, two-phase culture systems can be broadly categorised as liquid-liquid or liquid-solid. The choice of material for the second phase depends on the type of compound to be recovered and the compatibility with the other phase. Different factors affecting the efficiency of two-phase culture systems include the choice of material for the secondary phase, its concentration, volume, and time of addition. Factors such as cell elicitation, immobilization, and permeabilization, have been suggested as important strategies to make the two-phase culture system practically reliable on a commercial scale. Since there are many possibilities for designing a two-phase system, more detailed studies are needed to broaden the range of secondary phases compatible with the various plant species producing SMs with potential applications, mainly in the food and pharmacology industries.
Stratified coastal ocean interactions with tropical cyclones
Glenn, S. M.; Miles, T. N.; Seroka, G. N.; Xu, Y.; Forney, R. K.; Yu, F.; Roarty, H.; Schofield, O.; Kohut, J.
2016-01-01
Hurricane-intensity forecast improvements currently lag the progress achieved for hurricane tracks. Integrated ocean observations and simulations during hurricane Irene (2011) reveal that the wind-forced two-layer circulation of the stratified coastal ocean, and resultant shear-induced mixing, led to significant and rapid ahead-of-eye-centre cooling (at least 6 °C and up to 11 °C) over a wide swath of the continental shelf. Atmospheric simulations establish this cooling as the missing contribution required to reproduce Irene's accelerated intensity reduction. Historical buoys from 1985 to 2015 show that ahead-of-eye-centre cooling occurred beneath all 11 tropical cyclones that traversed the Mid-Atlantic Bight continental shelf during stratified summer conditions. A Yellow Sea buoy similarly revealed significant and rapid ahead-of-eye-centre cooling during Typhoon Muifa (2011). These findings establish that including realistic coastal baroclinic processes in forecasts of storm intensity and impacts will be increasingly critical to mid-latitude population centres as sea levels rise and tropical cyclone maximum intensities migrate poleward. PMID:26953963
Variance estimation for stratified propensity score estimators.
Williamson, E J; Morley, R; Lucas, A; Carpenter, J R
2012-07-10
Propensity score methods are increasingly used to estimate the effect of a treatment or exposure on an outcome in non-randomised studies. We focus on one such method, stratification on the propensity score, comparing it with the method of inverse-probability weighting by the propensity score. The propensity score--the conditional probability of receiving the treatment given observed covariates--is usually an unknown probability estimated from the data. Estimators for the variance of treatment effect estimates typically used in practice, however, do not take into account that the propensity score itself has been estimated from the data. By deriving the asymptotic marginal variance of the stratified estimate of treatment effect, correctly taking into account the estimation of the propensity score, we show that routinely used variance estimators are likely to produce confidence intervals that are too conservative when the propensity score model includes variables that predict (cause) the outcome, but only weakly predict the treatment. In contrast, a comparison with the analogous marginal variance for the inverse probability weighted (IPW) estimator shows that routinely used variance estimators for the IPW estimator are likely to produce confidence intervals that are almost always too conservative. Because exact calculation of the asymptotic marginal variance is likely to be complex, particularly for the stratified estimator, we suggest that bootstrap estimates of variance should be used in practice.
Analytical investigation of stratified isotropic media
NASA Astrophysics Data System (ADS)
Vytovtov, Konstantin A.
2005-04-01
A rigorous analytical approach for investigating a stratified medium with an arbitrary finite number of homogeneous isotropic layers in a period is developed. The approach is based on the translation matrix method. It is well known that the translation matrix for a period must be found as the product of the layer matrices. It is proved that this matrix can be represented as a finite sum of trigonometric matrices, and thus the dispersion relation of a stratified medium is written in an analytical form. All final expressions are obtained in terms of the constitutive parameters. To this author's knowledge, this is the first time that the new sign function that allows us to develop the presented analytical results has been described. The condition of the existence of a wave with an arbitrary period divisible by a structure period is found in analytical form. It is proved that changing the layer arrangement within the period does not affect the structure of the transmission and absorption bands.
Stratified and steady periodic water waves
NASA Astrophysics Data System (ADS)
Walsh, Samuel
This thesis considers two-dimensional stratified water waves propagating under the force of gravity over an impermeable at bed and with a free surface. In the absence of surface tension, it is proved that there exists of a global continuum of classical solutions that are periodic and traveling. These waves, moreover, can exhibit large density variation, speed, and amplitude. When the motion is assumed to be driven by capillarity on the surface and a gravitational force acting on the body of the fluid, it is shown that there exists global continua of such solutions. In both regimes, this is accomplished by first constructing a 1-parameter family of laminar flow solutions, then applying bifurcation theory methods to obtain local curves of small amplitude solutions branching from the laminar curve at an eigenvalue of the linearized problem. Each solution curve is then continued globally by means of a degree theoretic argument in the spirit of Rabinowitz. We also provide an alternate global bifurcation theorem via the analytic continuation method of Dancer. Finally, we consider the question of symmetry for two-dimensional stably stratified steady periodic gravity water waves with surface profiles monotonic between crests and troughs. We provide sufficient conditions under which such waves are necessarily symmetric. We do this by first exploiting some elliptic structure in the governing equations to show that, in certain size regimes, a maximum principle holds. This then forms the basis for a method of moving planes argument.
Stratified coastal ocean interactions with tropical cyclones
NASA Astrophysics Data System (ADS)
Glenn, S. M.; Miles, T. N.; Seroka, G. N.; Xu, Y.; Forney, R. K.; Yu, F.; Roarty, H.; Schofield, O.; Kohut, J.
2016-03-01
Hurricane-intensity forecast improvements currently lag the progress achieved for hurricane tracks. Integrated ocean observations and simulations during hurricane Irene (2011) reveal that the wind-forced two-layer circulation of the stratified coastal ocean, and resultant shear-induced mixing, led to significant and rapid ahead-of-eye-centre cooling (at least 6 °C and up to 11 °C) over a wide swath of the continental shelf. Atmospheric simulations establish this cooling as the missing contribution required to reproduce Irene's accelerated intensity reduction. Historical buoys from 1985 to 2015 show that ahead-of-eye-centre cooling occurred beneath all 11 tropical cyclones that traversed the Mid-Atlantic Bight continental shelf during stratified summer conditions. A Yellow Sea buoy similarly revealed significant and rapid ahead-of-eye-centre cooling during Typhoon Muifa (2011). These findings establish that including realistic coastal baroclinic processes in forecasts of storm intensity and impacts will be increasingly critical to mid-latitude population centres as sea levels rise and tropical cyclone maximum intensities migrate poleward.
Anomalous diffusion in rotating stratified turbulence
NASA Astrophysics Data System (ADS)
Kimura, Yoshi; Herring, Jackson
2006-11-01
Diffusion in rotating and stratified fluids is one of the central subjects in geophysical and astrophysical dynamics. In this paper, we report features of the dispersion of Lagrangian fluid particles in rotating stratified flows using the Direct Numerical Simulations (DNS) of the Navier-Stokes equations. And for calculation of particle dispersion, we use the cubic spline interpolation method by Yeung and Pope. Our main concern is the picture different from the Taylor dispersion theory, i.e.
DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS
X. Wang; X. Sun; H. Zhao
2011-09-01
In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in
Two-phase systems: potential for in situ extraction of microalgal products.
Kleinegris, Dorinde M M; Janssen, Marcel; Brandenburg, Willem A; Wijffels, René H
2011-01-01
Algae are currently used for production of niche products and are becoming increasingly interesting for the production of bulk commodities, such as biodiesel. For the production of these goods to become economically feasible, production costs will have to be lowered by one order of magnitude. The application of two-phase systems could be used to lower production costs. These systems circumvent the costly step of cell harvesting, whilst the product is extracted and prepared for downstream processing. The mechanism of extraction is a fundamental aspect of the practical question whether two-phase systems can be applied for in situ extraction, viz, simultaneous growth, product formation and extraction, or as a separate downstream processing step. Three possible mechanisms are discussed; 1) product excretion 2) cell permeabilization, and 3) cell death. It was shown that in the case of product excretion, the application of two-phase systems for in situ extraction can be very valuable. With permeabilization and cell death, in situ extraction is not ideal, but the application of two-phase systems as downstream extraction steps can be part of a well-designed biorefinery process. In this way, processing costs can be decreased while the product is mildly and selectively extracted. Thus far none of the algal strains used in two-phase systems have been shown to excrete their product; the output has always been the result of cell death. Two-phase systems can be a good approach as a downstream processing step for these species. For future applications of two-phase in situ extraction in algal production processes, either new species that show product excretion should be discovered, or existing species should be modified to induce product excretion.
Determination and characteristics of the transition to two-phase slug flow in small channels
Wambsganss, M.W.; Jendrzejczyk, J.A.; France, D.M.
1992-12-01
Two-phase pressure drop was measured in a small horizontal rectangular channel (hydraulic diameter = 5.44 mm). The two-phase fluid was an air/water mixture at atmospheric pressure tested over a mass flux range of 50 to 2000 kg/m{sup 2}{center_dot}s. Two-phase flow patterns were identified and an objective method was found for determining the flow pattern transition from bubble or plug flow to slug flow. The method is based on an RMS pressure measurement. In particular, it is shown that the transition is accompanied by a clear and abrupt increase in the RMS pressure when plotted as a function of mass quality. Use of the RMS pressure as a two-phase flow pattern transition indicator is shown to have advantages over pressure-versus-time trace evaluations reported in the literature. The transition is substantiated by a clear local change in slope in the curve of two-phase pressure drop plotted as a function of either Martinelli parameter or mass quality. For high mass fluxes, the change in slope is distinguished by a local peak. Some degree of substantiation was found in previous work for both of the results (the RMS pressure change and the local pressure drop change) at the transition to slug flow.
Determination and characteristics of the transition to two-phase slug flow in small channels
Wambsganss, M.W.; Jendrzejczyk, J.A. ); France, D.M. . Dept. of Mechanical Engineering)
1992-01-01
Two-phase pressure drop was measured in a small horizontal rectangular channel (hydraulic diameter = 5.44 mm). The two-phase fluid was an air/water mixture at atmospheric pressure tested over a mass flux range of 50 to 2000 kg/m[sup 2][center dot]s. Two-phase flow patterns were identified and an objective method was found for determining the flow pattern transition from bubble or plug flow to slug flow. The method is based on an RMS pressure measurement. In particular, it is shown that the transition is accompanied by a clear and abrupt increase in the RMS pressure when plotted as a function of mass quality. Use of the RMS pressure as a two-phase flow pattern transition indicator is shown to have advantages over pressure-versus-time trace evaluations reported in the literature. The transition is substantiated by a clear local change in slope in the curve of two-phase pressure drop plotted as a function of either Martinelli parameter or mass quality. For high mass fluxes, the change in slope is distinguished by a local peak. Some degree of substantiation was found in previous work for both of the results (the RMS pressure change and the local pressure drop change) at the transition to slug flow.
Design and test of a mechanically pumped two-phase thermal control flight experiment
NASA Technical Reports Server (NTRS)
Grote, M. G.; Stark, J. A.; Butler, C. D.; Mcintosh, R.
1987-01-01
A flight experiment of a mechanically pumped two-phase ammonia thermal control system, incorporating a number of new component designs, has been assembled and tested in a 1-g environment. Additional microgravity tests are planned on the Space Shuttle when Shuttle flights are resumed. The primary purpose of this experiment is to evaluate the operation of a mechanically pumped two-phase ammonia system, with emphasis on determining the performance of an evaporative Two-Phase Mounting Plate. The experiment also evaluates the performance of other specially designed components, such as the two-phase reservoir for temperature control, condensing radiator/heat sink, spiral tube boiler, and pressure drop experiment. The 1-g tests have shown that start-up of the two-phase experiment is easily accomplished with only a partial fill of ammonia. The experiment maintained a constant mounting plate temperature without flow rate controls over a very wide range of heat loads, flow rates, inlet flow conditions and exit qualities. The tests also showed the successful operation of the mounting plate in the heat sharing condensing mode.
A new two-phase erosion-deposition model for mass flows
NASA Astrophysics Data System (ADS)
Pudasaini, Shiva P.; Fischer, Jan-Thomas
2016-04-01
Erosion, entrainment and deposition are complex and dominant, but yet poorly understood, mechanical processes in geophysical mass flows. Here, we propose a novel, two-phase, erosion-deposition model capable of adequately describing these complex phenomena commonly observed in landslides, avalanches, debris flows and bedload transports. The model enhances an existing general two-phase mass flow model (Pudasaini, 2012) by introducing a two-phase variably saturated erodible basal morphology. The adaptive basal morphology allows for the evolution of erosion-deposition-depths, incorporating the inherent physical process and rheological changes of the flowing mixture. With rigorous derivation, we show that appropriate incorporation of the mass and momentum productions and losses in conservative model formulation is essential for the physically correct and mathematically consistent description of erosion-entrainment-deposition processes. Simulation indicates a sharp erosion-front and steady-state-rear erosion depth. The model appropriately captures the emergence and propagation of complex frontal surge dynamics associated with the frontal ambient-drag which is a new hypothesis associated with erosion. The novel enhanced real two-phase model also allows for simulating fluid-run-off during the deposition process. The model resembles laboratory experiments for particle-fluid mixture flows and reveals some major aspects of the mechanics associated with erosion, entrainment and deposition. Reference: Shiva P. Pudasaini (2012): A general two-phase debris flow model. J. Geophys. Res., 117, F03010, doi: 10.1029/2011JF002186.
Simulation of two-phase flow using lattice gas automata methods
Tsumaya, Akira; Ohashi, Hirotada; Akiyama, Mamoru
1996-08-01
Two-phase flow simulation has been primarily based on experimental data in the sense that constitutive relations necessary for solving fundamental equations are experimentally determined. This assures validity of simulation of two-phase flow within the experimental conditions, but it is difficult to predict the behavior of two-phase flow under extreme or complex conditions which occur, for example, in severe accidents of nuclear reactors. Lattice gas automaton (LGA) simulation has recently attracted attention as a method for numerical simulation of multi phase flow. The authors extend phase-separation LGA models and develop methods for two-phase flow simulation. First, they newly added a flow model to the immiscible lattice gas model and applied it to two-dimensional Poiseuille flow. They obtained a result looking like lubricated pipelining of crude oil with water. Also, considering the gravity effect, they introduced a buoyancy force into the liquid-gas model. As a result, they demonstrated that gas bubbles of various diameters rise and gradually coalesce each other turning into larger bubbles. Using these newly developed LGA models, they succeeded in simulating various flow patterns of two-phase flow.
Deledicque, Vincent; Papalexandris, Miltiadis V.
2008-11-10
In this article, we present and analyze a conservative approximation to reduced one-pressure one-velocity models for compressible two-phase flows that contain non-conservative products. This approximation is valid when certain material properties of the two phases are considerably different from each other. Although it cannot be applied to arbitrary mixtures, it is applicable to many heterogeneous mixtures of technological interest. Herein, we derive the Rankine-Hugoniot relations and Riemann invariants for the homogeneous part of the proposed model and develop an exact Riemann solver for it. Further, we investigate the structure of the steady two-phase detonation waves, with inert or reactive solid particles, admitted by the proposed model. Comparisons with the corresponding gaseous detonations are also made. Moreover, we derive a lower limit for the propagation speed of steady two-phase detonations in the case of reactive particles. At the limiting case of very dilute mixtures, this minimum speed tends to the Chapman-Jouguet velocity of gaseous detonations. Finally, we report on numerical simulations of the transmission of a purely gaseous detonation to heterogeneous mixtures containing inert or reactive solid particles. The effect of the solid particles on the structure of the resulting two-phase detonation is discussed in detail.
DSMC simulation of two-phase plume flow with UV radiation
Li, Jie; Liu, Ying; Wang, Ning; Jin, Ling
2014-12-09
Rarefied gas-particle two-phase plume in which the phase of particles is liquid or solid flows from a solid propellant rocket of hypersonic vehicle flying at high altitudes, the aluminum oxide particulates not only impact the rarefied gas flow properties, but also make a great difference to plume radiation signature, so the radiation prediction of the rarefied gas-particle two-phase plume flow is very important for space target detection of hypersonic vehicles. Accordingly, this project aims to study the rarefied gas-particle two-phase flow and ultraviolet radiation (UV) characteristics. Considering a two-way interphase coupling of momentum and energy, the direct simulation Monte Carlo (DSMC) method is developed for particle phase change and the particle flow, including particulate collision, coalescence as well as separation, and a Monte Carlo ray trace model is implemented for the particulate UV radiation. A program for the numerical simulation of the gas-particle two-phase flow and radiation in which the gas flow nonequilibrium is strong is implemented as well. Ultraviolet radiation characteristics of the particle phase is studied based on the calculation of the flow field coupled with the radiation calculation, the radiation model for different size particles is analyzed, focusing on the effects of particle emission, absorption, scattering as well as the searchlight emission of the nozzle. A new approach may be proposed to describe the rarefied gas-particle two-phase plume flow and radiation transfer characteristics in this project.
Experimental and Analytical Study of Two-Phase Flow in Microgravity
NASA Technical Reports Server (NTRS)
McQuillen, John B.; Abdollahian, Davood; Quintal, J.; Zahm, J.
1996-01-01
Design of the two-phase flow systems which are anticipated to be utilized in future spacecraft thermal management systems requires a knowledge of two-phase flow and heat transfer parameters in reduced gravities. A program has been initiated by NASA to design a two-phase test loop and to perform a series of experiments to study the effect of gravity on the Critical Heat Flux (CHF) and onset of instability. The test loop is also instrumented to generate data for two-phase pressure drop. In addition to low gravity airplane trajectory testing, the experimental program consisted of a set of laboratory tests which were intended to generate data under the bounding conditions (+1 g and -1 g) in order to plan the test matrix. One set of airplane trajectory tests has been performed and several modifications to the test set-up have been identified. Preliminary test results have been used to demonstrate the applicability of the earth gravity models for prediction of the two-phase friction pressure drop.
Scaling of Two-Phase Flows to Partial-Earth Gravity
NASA Technical Reports Server (NTRS)
Hurlbert, Kathryn M.; Witte, Larry C.
2003-01-01
A report presents a method of scaling, to partial-Earth gravity, of parameters that describe pressure drops and other characteristics of two-phase (liquid/ vapor) flows. The development of the method was prompted by the need for a means of designing two-phase flow systems to operate on the Moon and on Mars, using fluid-properties and flow data from terrestrial two-phase-flow experiments, thus eliminating the need for partial-gravity testing. The report presents an explicit procedure for designing an Earth-based test bed that can provide hydrodynamic similarity with two-phase fluids flowing in partial-gravity systems. The procedure does not require prior knowledge of the flow regime (i.e., the spatial orientation of the phases). The method also provides for determination of pressure drops in two-phase partial-gravity flows by use of a generalization of the classical Moody chart (previously applicable to single-phase flow only). The report presents experimental data from Mars- and Moon-activity experiments that appear to demonstrate the validity of this method.
New Results in Two-Phase Pressure Drop Calculations at Reduced Gravity Conditions
NASA Astrophysics Data System (ADS)
Braisted, Jon; Kurwitz, Cable; Best, Frederick
2004-02-01
The mass, power, and volume energy savings of two-phase systems for future spacecraft creates many advantages over current single-phase systems. Current models of two-phase phenomena such as pressure drop, void fraction, and flow regime prediction are still not well defined for space applications. Commercially available two-phase modeling software has been developed for a large range of acceleration fields including reduced-gravity conditions. Recently, a two-phase experiment has been flown to expand the two-phase database. A model of the experiment was created in the software to determine how well the software could predict the pressure drop observed in the experiment. Of the simulations conducted, the computer model shows good agreement of the pressure drop in the experiment to within 30%. However, the software does begin to over-predict pressure drop in certain regions of a flow regime map indicating that some models used in the software package for reduced-gravity modeling need improvement.
Gas-liquid two-phase flow across a bank of micropillars
NASA Astrophysics Data System (ADS)
Krishnamurthy, Santosh; Peles, Yoav
2007-04-01
Adiabatic nitrogen-water two-phase flow across a bank of staggered circular micropillars, 100μm long with a diameter of 100μm and a pitch-to-diameter ratio of 1.5, was investigated experimentally for Reynolds number ranging from 5 to 50. Flow patterns, void fraction, and pressure drop were obtained, discussed, and compared to large scale as well as microchannel results. Two-phase flow patterns were determined by flow visualization, and a flow map was constructed as a function of gas and liquid superficial velocities. Significant deviations from conventional scale systems, with respect to flow patterns and trend lines, were observed. A unique flow pattern, driven by surface tension, was observed and termed bridge flow. The applicability of conventional scale models to predict the void fraction and two-phase frictional pressure drop was also assessed. Comparison with a conventional scale void fraction model revealed good agreement, but was found to be in a physically wrong form. Thus, a modified physically based model for void fraction was developed. A two-phase frictional multiplier was found to be a strong function of mass flux, unlike in previous microchannel studies. It was observed that models from conventional scale systems did not adequately predict the two-phase frictional multiplier at the microscale, thus, a modified model accounting for mass flux was developed.
Pointer, William David; Shaver, Dillon; Liu, Yang; Vegendla, Prasad; Tentner, Adrian
2016-09-30
The U.S. Department of Energy, Office of Nuclear Energy charges participants in the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program with the development of advanced modeling and simulation capabilities that can be used to address design, performance and safety challenges in the development and deployment of advanced reactor technology. The NEAMS has established a high impact problem (HIP) team to demonstrate the applicability of these tools to identification and mitigation of sources of steam generator flow induced vibration (SGFIV). The SGFIV HIP team is working to evaluate vibration sources in an advanced helical coil steam generator using computational fluid dynamics (CFD) simulations of the turbulent primary coolant flow over the outside of the tubes and CFD simulations of the turbulent multiphase boiling secondary coolant flow inside the tubes integrated with high resolution finite element method assessments of the tubes and their associated structural supports. This report summarizes the demonstration of a methodology for the multiphase boiling flow analysis inside the helical coil steam generator tube. A helical coil steam generator configuration has been defined based on the experiments completed by Polytecnico di Milano in the SIET helical coil steam generator tube facility. Simulations of the defined problem have been completed using the Eulerian-Eulerian multi-fluid modeling capabilities of the commercial CFD code STAR-CCM+. Simulations suggest that the two phases will quickly stratify in the slightly inclined pipe of the helical coil steam generator. These results have been successfully benchmarked against both empirical correlations for pressure drop and simulations using an alternate CFD methodology, the dispersed phase mixture modeling capabilities of the open source CFD code Nek5000.
Clustering of floating particles in stratified turbulence
NASA Astrophysics Data System (ADS)
Boffetta, Guido; de Lillo, Filippo; Musacchio, Stefano; Sozza, Alessandro
2016-11-01
We study the dynamics of small floating particles transported by stratified turbulence in presence of a mean linear density profile as a simple model for the confinement and the accumulation of plankton in the ocean. By means of extensive direct numerical simulations we investigate the statistical distribution of floaters as a function of the two dimensionless parameters of the problem. We find that vertical confinement of particles is mainly ruled by the degree of stratification, with a weak dependency on the particle properties. Conversely, small scale fractal clustering, typical of non-neutral particles in turbulence, depends on the particle relaxation time and is only weakly dependent on the flow stratification. The implications of our findings for the formation of thin phytoplankton layers are discussed.
Defining drug response for stratified medicine.
Lonergan, Mike; Senn, Stephen J; McNamee, Christine; Daly, Ann K; Sutton, Robert; Hattersley, Andrew; Pearson, Ewan; Pirmohamed, Munir
2017-01-01
The premise for stratified medicine is that drug efficacy, drug safety, or both, vary between groups of patients, and biomarkers can be used to facilitate more targeted prescribing, with the aim of improving the benefit:risk ratio of treatment. However, many factors can contribute to the variability in response to drug treatment. Inadequate characterisation of the nature and degree of variability can lead to the identification of biomarkers that have limited utility in clinical settings. Here, we discuss the complexities associated with the investigation of variability in drug efficacy and drug safety, and how consideration of these issues a priori, together with standardisation of phenotypes, can increase both the efficiency of stratification procedures and identification of biomarkers with the potential for clinical impact.
Nonlinear internal waves in shallow stratified lakes
NASA Astrophysics Data System (ADS)
Kurkina, Oxana; Talipova, Tatiana; Kurkin, Andrey; Ruvinskaya, Ekaterina; Pelinovsky, Efim
2015-04-01
Weakly nonlinear model of internal waves based on the extended Korteweg-de Vries equation - Gardner equation is applied to analyze possible shapes in shallow stratified lake - Sankhar Lake, Russia. Series of temperature variation in space and time are collected and analyzed. The spectra of such variations can be fitted by power function of frequency with exponent minus one, minus two. It is shown that temperature variations influence on kinematic characteristics of internal waves, mainly on the coefficient of quadratic nonlinearity. The solitary wave (soliton) of the first mode is an elevation wave with amplitude less 3 m (total depth of 15 m). The solitons of the second mode can have any polarity. Also the breathers of second mode can be generated in such lake.
Domain Growth Kinetics in Stratifying Foam Films
NASA Astrophysics Data System (ADS)
Zhang, Yiran; Sharma, Vivek
2015-03-01
Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Typical foam films consist of two surfactant-laden surfaces that are μ 5 nm - 10 micron apart. Sandwiched between these interfacial layers is a fluid that drains primarily under the influence of viscous and interfacial forces, including disjoining pressure. Interestingly, for certain low molecular weight surfactants, a layered ordering of micelles inside the foam films (thickness <100 nm) leads to a stepwise thinning phenomena called stratification. We experimentally elucidate the influence of these different driving forces, and confinement on drainage kinetics of horizontal stratifying foam films. Thinner, darker domains spontaneously grow within foam films. Quantitative characterization of domain growth visualized in a using Scheludko-type thin film cell and a theoretical model based on lubrication analysis, provide critical insights into hydrodynamics of thin foam films, and the strength and nature of surface forces, including supramolecular oscillatory structural forces.
Laminar flame propagation in a stratified charge
NASA Astrophysics Data System (ADS)
Ra, Youngchul
The propagation of laminar flame from a rich or stoichiometric mixture to a lean mixture in a stratified methane-air charge was investigated experimentally and numerically. Emphasis was on the understanding of the flame behavior in the transition region; in particular, on the mechanism of burning velocity enhancement in this region. In the experimental setup, mixtures of two different equivalence ratios were separated by a soap bubble in a spherical constant volume combustion vessel. The richer mixture inside the bubble was ignited by a focused laser beam. The flame development was observed by Schlieren technique and flame speeds were measured by heat release analysis of the pressure data. An one-dimensional, time- dependant numerical simulation of the flame propagation in a charge with step-stratification was used to interpret the experimental results. Both the experimental and numerical studies showed that the instantaneous flame speed depended on the previous flame history. Thus a `strong' (with mixture equivalence ratio close to stoichiometric) flame can sustain propagation into finite regions of substantially lean equivalence ratio. Both thermal and chemical effects were crucial for explaining the mechanism of the flame speed enhancement in the transition period. Because of the presence of this `back- support' effect, the usual concept of specifying the burning velocity as a function of the end gas state is inadequate for a stratified charge. A simple correlation for instantaneous flame velocity based on the local burned gas temperature is developed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.)
Stratified charge rotary engine combustion studies
NASA Technical Reports Server (NTRS)
Shock, H.; Hamady, F.; Somerton, C.; Stuecken, T.; Chouinard, E.; Rachal, T.; Kosterman, J.; Lambeth, M.; Olbrich, C.
1989-01-01
Analytical and experimental studies of the combustion process in a stratified charge rotary engine (SCRE) continue to be the subject of active research in recent years. Specifically to meet the demand for more sophisticated products, a detailed understanding of the engine system of interest is warranted. With this in mind the objective of this work is to develop an understanding of the controlling factors that affect the SCRE combustion process so that an efficient power dense rotary engine can be designed. The influence of the induction-exhaust systems and the rotor geometry are believed to have a significant effect on combustion chamber flow characteristics. In this report, emphasis is centered on Laser Doppler Velocimetry (LDV) measurements and on qualitative flow visualizations in the combustion chamber of the motored rotary engine assembly. This will provide a basic understanding of the flow process in the RCE and serve as a data base for verification of numerical simulations. Understanding fuel injection provisions is also important to the successful operation of the stratified charge rotary engine. Toward this end, flow visualizations depicting the development of high speed, high pressure fuel jets are described. Friction is an important consideration in an engine from the standpoint of lost work, durability and reliability. MSU Engine Research Laboratory efforts in accessing the frictional losses associated with the rotary engine are described. This includes work which describes losses in bearing, seal and auxillary components. Finally, a computer controlled mapping system under development is described. This system can be used to map shapes such as combustion chamber, intake manifolds or turbine blades accurately.
Stratified Sampling Design Based on Data Mining
Kim, Yeonkook J.; Oh, Yoonhwan; Park, Sunghoon; Cho, Sungzoon
2013-01-01
Objectives To explore classification rules based on data mining methodologies which are to be used in defining strata in stratified sampling of healthcare providers with improved sampling efficiency. Methods We performed k-means clustering to group providers with similar characteristics, then, constructed decision trees on cluster labels to generate stratification rules. We assessed the variance explained by the stratification proposed in this study and by conventional stratification to evaluate the performance of the sampling design. We constructed a study database from health insurance claims data and providers' profile data made available to this study by the Health Insurance Review and Assessment Service of South Korea, and population data from Statistics Korea. From our database, we used the data for single specialty clinics or hospitals in two specialties, general surgery and ophthalmology, for the year 2011 in this study. Results Data mining resulted in five strata in general surgery with two stratification variables, the number of inpatients per specialist and population density of provider location, and five strata in ophthalmology with two stratification variables, the number of inpatients per specialist and number of beds. The percentages of variance in annual changes in the productivity of specialists explained by the stratification in general surgery and ophthalmology were 22% and 8%, respectively, whereas conventional stratification by the type of provider location and number of beds explained 2% and 0.2% of variance, respectively. Conclusions This study demonstrated that data mining methods can be used in designing efficient stratified sampling with variables readily available to the insurer and government; it offers an alternative to the existing stratification method that is widely used in healthcare provider surveys in South Korea. PMID:24175117
Stratified scaffold design for engineering composite tissues.
Mosher, Christopher Z; Spalazzi, Jeffrey P; Lu, Helen H
2015-08-01
A significant challenge to orthopaedic soft tissue repair is the biological fixation of autologous or allogeneic grafts with bone, whereby the lack of functional integration between such grafts and host bone has limited the clinical success of anterior cruciate ligament (ACL) and other common soft tissue-based reconstructive grafts. The inability of current surgical reconstruction to restore the native fibrocartilaginous insertion between the ACL and the femur or tibia, which minimizes stress concentration and facilitates load transfer between the soft and hard tissues, compromises the long-term clinical functionality of these grafts. To enable integration, a stratified scaffold design that mimics the multiple tissue regions of the ACL interface (ligament-fibrocartilage-bone) represents a promising strategy for composite tissue formation. Moreover, distinct cellular organization and phase-specific matrix heterogeneity achieved through co- or tri-culture within the scaffold system can promote biomimetic multi-tissue regeneration. Here, we describe the methods for fabricating a tri-phasic scaffold intended for ligament-bone integration, as well as the tri-culture of fibroblasts, chondrocytes, and osteoblasts on the stratified scaffold for the formation of structurally contiguous and compositionally distinct regions of ligament, fibrocartilage and bone. The primary advantage of the tri-phasic scaffold is the recapitulation of the multi-tissue organization across the native interface through the layered design. Moreover, in addition to ease of fabrication, each scaffold phase is similar in polymer composition and therefore can be joined together by sintering, enabling the seamless integration of each region and avoiding delamination between scaffold layers.
Ong, C.L.; Thome, J.R.
2011-01-15
The classification of macroscale, mesoscale and microscale channels with respect to two-phase processes is still an open question. The main objective of this study focuses on investigating the macro-to-microscale transition during flow boiling in small scale channels of three different sizes with three different refrigerants over a range of saturation conditions to investigate the effects of channel confinement on two-phase flow patterns and liquid film stratification in a single circular horizontal channel (Part 2 covers the flow boiling heat transfer and critical heat flux). This paper presents the experimental two-phase flow pattern transition data together with a top/bottom liquid film thickness comparison for refrigerants R134a, R236fa and R245fa during flow boiling in small channels of 1.03, 2.20 and 3.04 mm diameter. Based on this work, an improved flow pattern map has been proposed by determining the flow patterns transitions existing under different conditions including the transition to macroscale slug/plug flow at a confinement number of Co {approx} 0.3-0.4. From the top/bottom liquid film thickness comparison results, it was observed that the gravity forces are fully suppressed and overcome by the surface tension and shear forces when the confinement number approaches 1, Co {approx} 1. Thus, as a new approximate rule, the lower threshold of macroscale flow is Co = 0.3-0.4 while the upper threshold of symmetric microscale flow is Co {approx} 1 with a transition (or mesoscale) region in-between. (author)
The bubbly-slug transition in a boiling two-phase flow under microgravity
NASA Technical Reports Server (NTRS)
Kiper, Ali M.; Swanson, T. D.
1993-01-01
A theory is presented to describe, in reduced gravity flow boiling, the transition from bubbly two-phase flow to slug flow. It is shown that characteristics of the bubbly flow and the transition were controlled by the mechanism of vapor bubble growth dynamics. By considering in nucleate boiling, behavior of vapor bubbles at departure from a heated surface a condition required for transition was determined. Although required, this condition alone could not ensure coalescence of bubbles to cause the transition to slug two-phase flow. The condition leading to coalescence, therefore, was obtained by examining oscillations of vapor bubbles following their departure from the heated surface. The predicted transition conditions were compared with the prediction and test data reported for adiabatic reduced gravity two-phase flow, and good qualitative agreement was found.
Dynamics of face and annular seals with two-phase flow
NASA Technical Reports Server (NTRS)
Hughes, William F.; Basu, Prithwish; Beatty, Paul A.; Beeler, Richard M.; Lau, Stephen
1988-01-01
A detailed study was made of face and annular seals under conditions where boiling, i.e., phase change of the leaking fluid, occurs within the seal. Many seals operate in this mode because of flashing due to pressure drop and/or heat input from frictional heating. Some of the distinctive behavior characteristics of two phase seals are discussed, particularly their axial stability. The main conclusions are that seals with two phase flow may be unstable if improperly balanced. Detailed theoretical analyses of low (laminar) and high (turbulent) leakage seals are presented along with computer codes, parametric studies, and in particular a simplified PC based code that allows for rapid performance prediction: calculations of stiffness coefficients, temperature and pressure distributions, and leakage rates for parallel and coned face seals. A simplified combined computer code for the performance prediction over the laminar and turbulent ranges of a two phase flow is described and documented. The analyses, results, and computer codes are summarized.
Investigation of two-phase heat transfer coefficients of argon-freon cryogenic mixed refrigerants
NASA Astrophysics Data System (ADS)
Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon
2014-11-01
Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon-freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.
Device for measuring the fluid density of a two-phase mixture
Cole, Jack H.
1980-01-01
A device for measuring the fluid density of a two-phase mixture flowing through a tubular member. A rotor assembly is rotatively supported within the tubular member so that it can also move axially within the tubular member. The rotor assembly is balanced against a pair of springs which exert an axial force in the opposite direction upon the rotor assembly. As a two-phase mixture flows through the tubular member it contacts the rotor assembly causing it to rotate about its axis. The rotor assembly is forced against and partially compresses the springs. Means are provided to measure the rotational speed of the rotor assembly and the linear displacement of the rotor assembly. From these measurements the fluid density of the two-phase mixture is calculated.
Two-Phase Master Sintering Curve for 17-4 PH Stainless Steel
NASA Astrophysics Data System (ADS)
Jung, Im Doo; Ha, Sangyul; Park, Seong Jin; Blaine, Deborah C.; Bollina, Ravi; German, Randall M.
2016-11-01
The sintering behavior of 17-4 PH stainless steel has been efficiently characterized by a two-phase master sintering curve model (MSC). The activation energy for the sintering of gas-atomized and water-atomized 17-4 PH powders is derived using the mean residual method, and the relative density of both powders is well predicted by the two-phase MSC model. The average error between dilatometry data and MSC model has been reduced by 68 pct for gas-atomized powder and by 45 pct for water-atomized powder through the consideration of phase transformation of 17-4 PH in MSC model. The effect of δ-ferrite is considered in the two-phase MSC model, leading to excellent explanation of the sintering behavior for 17-4 PH stainless steel. The suggested model is useful in predicting the densification and phase change phenomenon during sintering of 17-4 PH stainless steel.
Two-phase pressure drop across a hydrofoil-based micro pin device using R-123
Kosar, Ali
2008-05-15
The two-phase pressure drop in a hydrofoil-based micro pin fin heat sink has been investigated using R-123 as the working fluid. Two-phase frictional multipliers have been obtained over mass fluxes from 976 to 2349 kg/m{sup 2} s and liquid and gas superficial velocities from 0.38 to 1.89 m/s and from 0.19 to 24 m/s, respectively. It has been found that the two-phase frictional multiplier is strongly dependent on flow pattern. The theoretical prediction using Martinelli parameter based on the laminar fluid and laminar gas flow represented the experimental data fairly well for the spray-annular flow. For the bubbly and wavy-intermittent flow, however, large deviations from the experimental data were recorded. The Martinelli parameter was successfully used to determine the flow patterns, which were bubbly, wavy-intermittent, and spray-annular flow in the current study. (author)
Two-phase region of vortex-solid melting: 3D XY theory
NASA Astrophysics Data System (ADS)
Friesen, M.; Muzikar, P.
1998-07-01
In clean enough samples of the high-Tc oxide materials, the phase transition into the superconducting state occurs along a first-order line in the H-T plane. This means that a two-phase region occurs in the B-T plane, in which the liquid and solid vortex phases coexist. We discuss the thermodynamics of this two-phase region, developing formulae relating experimental quantities of interest. We then apply the 3D XY scaling theory to the problem, obtaining detailed predictions for the boundaries of the coexistence region. By using published data, we are able to predict the width of the two-phase region, and determine the physical parameters involved in the 3D XY description.
Reduced-gravity two-phase flow experiments in the NASA KC-135
NASA Technical Reports Server (NTRS)
Cuta, Judith M.; Michener, Thomas E.; Best, Frederick R.; Kachnik, Leo J.
1988-01-01
An adequate understanding is sought of flow and heat transfer behavior in reduced and zero gravity conditions. Microgravity thermal-hydraulic analysis capabilities were developed for application to space nuclear power systems. A series of reduced gravity two phase flow experiments using the NASA KC-135 were performed. The objective was to supply basic thermal hydraulic information that could be used in development of analytical tools for design of space power systems. The experiments are described. Two main conclusions were drawn. First, the tests demonstrate that the KC-135 is a suitable test environment for obtaining two phase flow and heat transfer data in reduced gravity conditions. Second, the behavior of two phase flow in low gravity is sufficiently different from that obtained in 1 g to warrant intensive investigation of the phenomenon if adequate analytical tools are to be developed for microgravity conditions.
Two-phase flow characterization for fluid components and variable gravity conditions
NASA Technical Reports Server (NTRS)
Dzenitis, John M.; Miller, Kathryn M.
1992-01-01
This paper describes a program initiated by the NASA Johnson Space Center to investigate vapor-liquid flow regimes and pressure drops in pipe components and variable gravity conditions. This program supports the Space Station Freedom External Active Thermal Control System design and future space missions, including the Space Exploration Initiative activities. The objectives for this program include studying two-phase flow behavior in fluid components (smooth pipes, bellows lines, quick-disconnect fittings), expanding the two-phase database for zero-g conditions, developing a database for low-g conditions (for example, Moon-g, Mars-g), and validating models for two-phase flow analyses. Zero-g and low-g data will be gathered using a Freon-12 flow loop during four test series on the KC-135 aircraft beginning in August 1991.
Entropy analysis on non-equilibrium two-phase flow models
Karwat, H.; Ruan, Y.Q.
1995-09-01
A method of entropy analysis according to the second law of thermodynamics is proposed for the assessment of a class of practical non-equilibrium two-phase flow models. Entropy conditions are derived directly from a local instantaneous formulation for an arbitrary control volume of a structural two-phase fluid, which are finally expressed in terms of the averaged thermodynamic independent variables and their time derivatives as well as the boundary conditions for the volume. On the basis of a widely used thermal-hydraulic system code it is demonstrated with practical examples that entropy production rates in control volumes can be numerically quantified by using the data from the output data files. Entropy analysis using the proposed method is useful in identifying some potential problems in two-phase flow models and predictions as well as in studying the effects of some free parameters in closure relationships.
Air/water two-phase flow test tunnel for airfoil studies
NASA Astrophysics Data System (ADS)
Ohashi, H.; Matsumoto, Y.; Ichikawa, Y.; Tsukiyama, T.
1990-02-01
A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.
Air/water two-phase flow test tunnel for airfoil studies
NASA Astrophysics Data System (ADS)
Ohashi, H.; Matsumoto, Y.; Ichikawa, Y.; Tsukiyama, T.
1994-01-01
A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.
Electrical impedance string probes for two-phase void and velocity measurements. [PWR
Hardy, J E; Hylton, J O
1982-05-01
An instrumentation scheme has been developed to measure two-phase flow velocity and void fraction during the refill/reflood stages of a loss-of-coolant accident in experimental test facilities. The instrumentation's principle of operation was based on measurement of the electrical impedance of two-phase mixtures. Two-phase velocity is estimated by time-of-flight analysis of signals from two spatially separate sensors. A relative capacitive technique was employed to measure void fraction. The impedance sensor consists of a pair of stainless steel wires strung back and forth across a stainless steel frame. This sensor was dubbed string probe for this reason. The string probe was designed to withstand temperatures of 350/sup 0/C, thermal transients of approx. 300/sup 0/C/s, and severe fluid- and condensation-induced shocks.
Magnetic liquid metal two-phase flow research. Phase 1. Final report
Graves, R.D.
1983-04-01
The Phase I research demonstrates the feasibility of the magnetic liquid metal (MLM) two-phase flow concept. A dispersion analysis is presented based on a complete set of two-phase-flow equations augmented to include stresses due to magnetic polarization of the fluid. The analysis shows that the stability of the MLM two-phase flow is determined by the magnetic Mach number, the slip ratio, geometry of the flow relative to the applied magnetic field, and by the voidage dependence of the interfacial forces. Results of a set of experiments concerned with magnetic effects on the dynamics of single bubble motion in an aqueous-based, viscous, conducting magnetic fluid are presented. Predictions in the theoretical literature are qualitatively verified using a bench-top experimental apparatus. In particular, applied magnetic fields are seen to lead to reduced bubble size at fixed generating orifice pressure.
Numerical simulation and analysis of solid-liquid two-phase flow in centrifugal pump
NASA Astrophysics Data System (ADS)
Zhang, Yuliang; Li, Yi; Cui, Baoling; Zhu, Zuchao; Dou, Huashu
2013-01-01
The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the two-phase flow pumps, i.e., low overall efficiency and severe abrasion. In this study, the three-dimensional, steady, incompressible, and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics (CFD) code based on the mixture model of the two-phase flow and the RNG k- ɛ two-equation turbulence model, in which the influences of rotation and curvature are fully taken into account. The coupling between impeller and volute is implemented by means of the frozen rotor method. The simulation results predicted indicate that the solid phase properties in two-phase flow, especially the concentration, the particle diameter and the density, have strong effects on the hydraulic performance of the pump. Both the pump head and the efficiency are reduced with increasing particle diameter or concentration. However, the effect of particle density on the performance is relatively minor. An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration. The suction side of the blade is subject to much more severe abrasion than the pressure side. The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump, and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.
NASA Astrophysics Data System (ADS)
Dong, S.
2014-06-01
We present an effective outflow boundary condition, and an associated numerical algorithm, within the phase-field framework for dealing with two-phase outflows or open boundaries. The set of two-phase outflow boundary conditions for the phase-field and flow variables are designed to prevent the un-controlled growth in the total energy of the two-phase system, even in situations where strong backflows or vortices may be present at the outflow boundaries. We also present an additional boundary condition for the phase field function, which together with the usual Dirichlet condition can work effectively as the phase-field inflow conditions. The numerical algorithm for dealing with these boundary conditions is developed on top of a strategy for de-coupling the computations of all flow variables and for overcoming the performance bottleneck caused by variable coefficient matrices associated with variable density/viscosity. The algorithm contains special constructions, for treating the variable dynamic viscosity in the outflow boundary condition, and for preventing a numerical locking at the outflow boundaries for time-dependent problems. Extensive numerical tests with incompressible two-phase flows involving inflow and outflow boundaries demonstrate that, the two-phase outflow boundary conditions and the numerical algorithm developed herein allow for the fluid interface and the two-phase flow to pass through the outflow or open boundaries in a smooth and seamless fashion, and that our method produces stable simulations when large density ratios and large viscosity ratios are involved and when strong backflows are present at the outflow boundaries.
Sub-critical two-phase seawater convection near a dike
NASA Astrophysics Data System (ADS)
Lowell, Robert P.; Xu, Wenyue
2000-01-01
We address the circulation of hydrothermal seawater near an igneous dike emplaced in the oceanic crust. By using the two-phase finite difference hydrothermal code GTHM, we are able to treat the sub-critical two-phase flow that occurs just after emplacement as well as the later single-phase circulation, which occurs as the dike cools. We investigate the effects of bulk rock permeability and dike width. The simulations show that for a 2 m wide dike emplaced in country rock with uniform permeability of 10 -9 m 2, two-phase flow may occur briefly adjacent to the dike margin in a region that is less than 0.1 m across. The width of the two-phase region and the duration of two-phase flow vary inversely with permeability, but they increase as the dike width increases. During two-phase flow, the advective heat flux at the seafloor fluctuates about its mean and the temperature near the seafloor remains nearly constant. The mean heat flux increases with permeability, but is independent of dike width. The model is used in conjunction with chlorinity data from 'A' vent near 9°N on the East Pacific Rise to indicate that the permeability there is ˜10 -12 m 2. The model suggests, however, that an additional heat source is required to account for the high-temperature vent fluids at 9°N that have persisted for more than 3 years. The calculations also show that heat transport near a high permeability dike (i.e., ≥10 -9 m 2) is consistent with the heat transport measured for the CoAxial event plumes. The calculations further suggest, however, that for a dike to generate an event plume, the zone of high permeability should be concentrated near the dike margin.
Characterization of annular two-phase gas-liquid flows in microgravity
NASA Astrophysics Data System (ADS)
Bousman, W. Scott; McQuillen, John B.
1994-08-01
A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.
Dynamics of face and annular seals with two-phase flow
NASA Technical Reports Server (NTRS)
Hughes, William F.; Basu, Prithwish; Beatty, Paul A.; Beeler, Richard M.; Lau, Stephen
1989-01-01
A detailed study was made of face and annular seals under conditions where boiling, i.e., phase change of the leaking fluid, occurs within the seal. Many seals operate in this mode because of flashing due to pressure drop and/or heat input from frictional heating. High pressure, water pumps, industrial chemical pumps, and cryogenic pumps are mentioned as a few of many applications. The initial motivation was the LOX-GOX seals for the space shuttle main engine, but the study was expanded to include any face or annular seal where boiling occurs. Some of the distinctive behavior characteristics of two-phase seals were discussed, particularly their axial stability. While two-phase seals probably exhibit instability to disturbances of other degrees of freedom such as wobble, etc., under certain conditions, such analyses are too complex to be treated at present. Since an all liquid seal (with parallel faces) has a neutral axial stiffness curve, and is stabilized axially by convergent coning, other degrees of freedom stability analyses are necessary. However, the axial stability behavior of the two-phase seal is always a consideration no matter how well the seal is aligned and regardless of the speed. Hence, axial stability is thought of as the primary design consideration for two-phase seals and indeed the stability behavior under sub-cooling variations probably overshadows other concerns. The main thrust was the dynamic analysis of axial motion of two-phase face seals, principally the determination of axial stiffness, and the steady behavior of two-phase annular seals. The main conclusions are that seals with two-phase flow may be unstable if improperly balanced. Detailed theoretical analyses of low (laminar) and high (turbulent) leakage seals are presented along with computer codes, parametric studies, and in particular a simplified PC based code that allows for rapid performance prediction. A simplified combined computer code for the performance prediction over the
Stochastic Discrete Equation Method (sDEM) for two-phase flows
Abgrall, R.; Congedo, P.M.; Geraci, G.; Rodio, M.G.
2015-10-15
A new scheme for the numerical approximation of a five-equation model taking into account Uncertainty Quantification (UQ) is presented. In particular, the Discrete Equation Method (DEM) for the discretization of the five-equation model is modified for including a formulation based on the adaptive Semi-Intrusive (aSI) scheme, thus yielding a new intrusive scheme (sDEM) for simulating stochastic two-phase flows. Some reference test-cases are performed in order to demonstrate the convergence properties and the efficiency of the overall scheme. The propagation of initial conditions uncertainties is evaluated in terms of mean and variance of several thermodynamic properties of the two phases.
On the peculiarities of LDA method in two-phase flows with high concentrations of particles
NASA Astrophysics Data System (ADS)
Poplavski, S. V.; Boiko, V. M.; Nesterov, A. U.
2016-10-01
Popular applications of laser Doppler anemometry (LDA) in gas dynamics are reviewed. It is shown that the most popular method cannot be used in supersonic flows and two-phase flows with high concentrations of particles. A new approach to implementation of the known LDA method based on direct spectral analysis, which offers better prospects for such problems, is presented. It is demonstrated that the method is suitable for gas-liquid jets. Owing to the progress in laser engineering, digital recording of spectra, and computer processing of data, the method is implemented at a higher technical level and provides new prospects of diagnostics of high-velocity dense two-phase flows.
Conceptual design of two-phase fluid mechanics and heat transfer facility for spacelab
NASA Technical Reports Server (NTRS)
North, B. F.; Hill, M. E.
1980-01-01
Five specific experiments were analyzed to provide definition of experiments designed to evaluate two phase fluid behavior in low gravity. The conceptual design represents a fluid mechanics and heat transfer facility for a double rack in Spacelab. The five experiments are two phase flow patterns and pressure drop, flow boiling, liquid reorientation, and interface bubble dynamics. Hardware was sized, instrumentation and data recording requirements defined, and the five experiments were installed as an integrated experimental package. Applicable available hardware was selected in the experiment design and total experiment program costs were defined.
Two-Phase Flow in Geothermal Wells: Development and Uses of a Good Computer Code
Ortiz-Ramirez, Jaime
1983-06-01
A computer code is developed for vertical two-phase flow in geothermal wellbores. The two-phase correlations used were developed by Orkiszewski (1967) and others and are widely applicable in the oil and gas industry. The computer code is compared to the flowing survey measurements from wells in the East Mesa, Cerro Prieto, and Roosevelt Hot Springs geothermal fields with success. Well data from the Svartsengi field in Iceland are also used. Several applications of the computer code are considered. They range from reservoir analysis to wellbore deposition studies. It is considered that accurate and workable wellbore simulators have an important role to play in geothermal reservoir engineering.
Film boiling on spheres in single- and two-phase flows. Final report
Liu, C.; Theofanous, T.G.
1994-12-01
Film boiling on spheres in single- and two-phase flows was studied experimentally and theoretically with an emphasis on establishing the film boiling heat transfer closure law, which is useful in the analysis of nuclear reactor core melt accidents. Systematic experimentation of film boiling on spheres in single-phase water flows was carried out to investigate the effects of liquid subcooling (from 0 to 40{degrees}C), liquid velocity (from 0 to 2 m/s), sphere superheat (from 200 to 900{degrees}C), sphere diameter (from 6 to 19 mm), and sphere material (stainless steel and brass) on film boiling heat transfer. Based on the experimental data a general film boiling heat transfer correlation is developed. Utilizing a two-phase laminar boundary-layer model for the unseparated front film region and a turbulent eddy model for the separated rear region, a theoretical model was developed to predict the film boiling heat transfer in all single-phase regimes. The film boiling from a sphere in two-phase flows was investigated both in upward two-phase flows (with void fraction from 0.2 to 0.65, water velocity from 0.6 to 3.2 m/s, and steam velocity from 3.0 to 9.0 m/s) and in downward two-phase flows (with void fraction from 0.7 to 0.95, water velocity from 1.9 to 6.5 m/s, and steam velocity from 1.1 to 9.0 m/s). The saturated single-phase heat transfer correlation was found to be applicable to the two-phase film boiling data by making use of the actual water velocity (water phase velocity), and an adjustment factor of (1-{alpha}){sup 1/4} (with {alpha} being the void fraction) for downward flow case only. Slight adjustments of the Reynolds number exponents in the correlation provided an even better interpretation of the two-phase data. Preliminary experiments were also conducted to address the influences of multisphere structure on the film boiling heat transfer in single- and two-phase flows.
Two-phase flow stability structure in a natural circulation system
Zhou, Zhiwei
1995-09-01
The present study reports a numerical analysis of two-phase flow stability structures in a natural circulation system with two parallel, heated channels. The numerical model is derived, based on the Galerkin moving nodal method. This analysis is related to some design options applicable to integral heating reactors with a slightly-boiling operation mode, and is also of general interest to similar facilities. The options include: (1) Symmetric heating and throttling; (2) Asymmetric heating and symmetric throttling; (3) Asymmetric heating and throttling. The oscillation modes for these variants are discussed. Comparisons with the data from the INET two-phase flow stability experiment have qualitatively validated the present analysis.
Two-dimensional Rarefaction Waves in the High-speed Two-phase Flow
NASA Astrophysics Data System (ADS)
Nakagawa, Masafumi; Harada, Atsushi
Two-phase flow nozzles are used in the total flow system for geothermal power plants and in the ejector of the refrigerant cycle, etc. One of the most important functions of a two-phase flow nozzle is to convert the thermal energy to the kinetic energy of the two-phase flow. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. There exist the shock waves or rarefaction waves at the outlet of a supersonic nozzle in the case of non-best fitting expansion conditions when the operation conditions of the nozzle are widely chosen. The purpose of the present study is to elucidate theoretically the character of the rarefaction waves at the outlet of the supersonic two-phase flow nozzle. Two-dimensional basic equations for the compressible two-phase flow are introduced considering the inter-phase momentum transfer. Sound velocities are obtained from these equations by using monochromatic wave approximation. Those depend on the relaxation time that determines the momentum transfer. The two-phase flow with large relaxation times has a frozen sound velocity, and with small one has an equilibrium sound velocity. Rarefaction waves which occurred behind the two-phase flow nozzle are calculated by the CIP method. Although the frozen Mach number, below one, controls these basic equations, the rarefaction waves appeared for small relaxation time. The Mach line behind which the expansion starts depends on the inlet velocity and the relaxation time. Those relationships are shown in this paper. The pressure expansion curves are only a function of the revolution angle around the corner of the nozzle outlet for the relaxation time less than 0.1. For the larger relaxation time, the pressure decays because of internal friction caused by inter phase momentum transfer, and the expansion curves are a function of not only the angle but also the flow direction. The calculated expansion curves are compared with the experimental ones
Characterization of annular two-phase gas-liquid flows in microgravity
NASA Technical Reports Server (NTRS)
Bousman, W. Scott; Mcquillen, John B.
1994-01-01
A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.
NASA Astrophysics Data System (ADS)
Wijethunga, Pavithra A. L.; Moon, Hyejin
2015-09-01
Aqueous two-phase systems (ATPSs) allow an advantageous aqueous two-phase extraction process (ATPE), a special type of liquid-liquid extraction. Compared with conventional liquid-liquid extraction using aqueous/organic extraction media, ATPE is known to provide relatively easy mass transfer and a gentle environment for biological separation applications. Considering the recent interest in microscale ATPE, we aimed to study (i) the potential of preparing ATPS droplets on a digital microfluidic device, and (ii) the influence of the fluidic dynamics created during the formation of ATPS, with the goal of enhancing on-chip ATPE process. On-chip ATPS formation was evaluated by preparing a series of ATPSs on electrowetting on dielectric digital microfluidic chips and comparing their characteristics with the same ATPSs prepared at macroscale using conventional procedures. An enhanced on-chip drop-to-drop ATPE process was achieved by incorporating a self-mixing condition created during ATPSformation. Results indicate a successful on-chip ATPS preparation as well as enhanced extraction performance by self-mixing in the absence of forced mixing. Findings of this research suggest an alternative, simple, yet adequate technique to provide mixing for on-chip applications, such as sample preparation in portable microfluidics, for which it is unfavorable to implement complicated mixing sequences or complex device geometries.
24 CFR 115.201 - The two phases of substantial equivalency certification.
Code of Federal Regulations, 2010 CFR
2010-04-01
... AND URBAN DEVELOPMENT FAIR HOUSING CERTIFICATION AND FUNDING OF STATE AND LOCAL FAIR HOUSING... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false The two phases of substantial equivalency certification. 115.201 Section 115.201 Housing and Urban Development Regulations Relating...
Aqueous polymer two-phase systems: effective tools for plasma membrane proteomics.
Schindler, Jens; Nothwang, Hans Gerd
2006-10-01
Plasma membranes (PMs) are of particular importance for all living cells. They form a selectively permeable barrier to the environment. Many essential tasks of PMs are carried out by their proteinaceous components, including molecular transport, cell-cell interactions, and signal transduction. Due to the key role of these proteins for cellular function, they take center-stage in basic and applied research. A major problem towards in-depth identification and characterization of PM proteins by modern proteomic approaches is their low abundance and immense heterogeneity in different cells. Highly selective and efficient purification protocols are hence essential to any PM proteome analysis. An effective tool for preparative isolation of PMs is partitioning in aqueous polymer two-phase systems. In two-phase systems, membranes are separated according to differences in surface properties rather than size and density. Despite their rare application to the fractionation of animal tissues and cells, they represent an attractive alternative to conventional fractionation protocols. Here, we review the principles of partitioning using aqueous polymer two-phase systems and compare aqueous polymer two-phase systems with other methods currently used for the isolation of PMs.
2013-11-01
state operation of the channel. Measurement and detection of changes in flow regime improve thermal management system modeling efforts. Historically...identification and classification of horizontal two-phase flow regimes relies on human interpretation of measured signals. Variations in flow...Tomography (ECT) is a non-invasive impedance measurement method that produces mean normalized permittivity ratio, ̅, values that are directly linked
Self-sustained hydrodynamic oscillations in a natural-circulation two-phase-flow boiling loop
NASA Technical Reports Server (NTRS)
Jain, K. C.
1969-01-01
Results of an experimental and theoretical study of factors affecting self-sustaining hydrodynamic oscillations in boiling-water loops are reported. Data on flow variables, and the effects of geometry, subcooling and pressure on the development of oscillatory behavior in a natural-circulation two-phase-flow boiling loop are included.
The two-phase extended evaluation in microgravity (TEEM) flight experiment: Description and overview
NASA Astrophysics Data System (ADS)
Hurlbert, Kathryn Miller
1997-01-01
The future missions of the National Aeronautics and Space Administration (NASA) may include orbiting satellites, orbiting platforms or stations, interplanetary vehicles, planetary surface missions, and planetary research probes. Current thermal control technology, using single-phase liquid coolant loops, is not a viable option for some of these future missions due to the associated power system weight and size penalty. Two-phase (liquid-vapor) flow thermal control systems can offer significant advantages over single-phase thermal systems in reducing the required power system mass and size. The Two-Phase Extended Evaluation in Microgravity (TEEM) Flight Experiment is currently being developed by NASA, and the Department of Defense (DOD) Space Test Program (STP) and the United States Air Force (USAF) Phillips Laboratory, with the cooperation of university researchers, to demonstrate operations of a closed-loop, two-phase system in a relevant mission environment. TEEM will also provide fully developed, two-phase flow data for zero-g conditions. This paper presents a description of the flight experiment, and a summary of the science of interest to the NASA Johnson Space Center (JSC).
An ALE Finite Element Approach for Two-Phase Flow with Phase Change
NASA Astrophysics Data System (ADS)
Gros, Erik; Anjos, Gustavo; Thome, John; Ltcm Team; Gesar Team
2016-11-01
In this work, two-phase flow with phase change is investigated through the Finite Element Method (FEM) in the Arbitrary Lagrangian-Eulerian (ALE) framework. The equations are discretized on an unstructured mesh where the interface between the phases is explicitly defined as a sub-set of the mesh. The two-phase interface position is described by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to very accurate results with moderate programming effort and computational costs. Such a methodology can be employed to study accurately many two-phase flow and heat transfer problems in industry such as oil extraction and refinement, design of refrigeration systems, modelling of microfluidic and biological systems and efficient cooling of electronics for computational purposes. The latter is the principal aim of the present research. The numerical results are discussed and compared to analytical solutions and reference results, thereby revealing the capability of the proposed methodology as a platform for the study of two-phase flow with phase change.
Mass and heat transport in the two-phase Buckley-Leverett model
NASA Astrophysics Data System (ADS)
Akhmetzyanov, Atlas V.; Kushner, Alexei G.; Lychagin, Valentin V.
2017-03-01
In this article we study the initial boundary value problem for two-phase heat and mass transport in porous media described by the Buckley-Leverett model. We outline a method to construct asymptotic solutions of the initial boundary problem and show how to overcome singularities in solutions and shock waves.
Comparison of Two-Phase Pipe Flow in OpenFOAM with a Mechanistic Model
NASA Astrophysics Data System (ADS)
Shuard, Adrian M.; Mahmud, Hisham B.; King, Andrew J.
2016-03-01
Two-phase pipe flow is a common occurrence in many industrial applications such as power generation and oil and gas transportation. Accurate prediction of liquid holdup and pressure drop is of vast importance to ensure effective design and operation of fluid transport systems. In this paper, a Computational Fluid Dynamics (CFD) study of a two-phase flow of air and water is performed using OpenFOAM. The two-phase solver, interFoam is used to identify flow patterns and generate values of liquid holdup and pressure drop, which are compared to results obtained from a two-phase mechanistic model developed by Petalas and Aziz (2002). A total of 60 simulations have been performed at three separate pipe inclinations of 0°, +10° and -10° respectively. A three dimensional, 0.052m diameter pipe of 4m length is used with the Shear Stress Transport (SST) k - ɷ turbulence model to solve the turbulent mixtures of air and water. Results show that the flow pattern behaviour and numerical values of liquid holdup and pressure drop compare reasonably well to the mechanistic model.
Approaches to myosin modelling in a two-phase flow model for cell motility
NASA Astrophysics Data System (ADS)
Kimpton, L. S.; Whiteley, J. P.; Waters, S. L.; Oliver, J. M.
2016-04-01
A wide range of biological processes rely on the ability of cells to move through their environment. Mathematical models have been developed to improve our understanding of how cells achieve motion. Here we develop models that explicitly track the cell's distribution of myosin within a two-phase flow framework. Myosin is a small motor protein which is important for contracting the cell's actin cytoskeleton and enabling cell motion. The two phases represent the actin network and the cytosol in the cell. We start from a fairly general description of myosin kinetics, advection and diffusion in the two-phase flow framework, then identify a number of sub-limits of the model that may be relevant in practice, two of which we investigate further via linear stability analyses and numerical simulations. We demonstrate that myosin-driven contraction of the actin network destabilizes a stationary steady state leading to cell motion, but that rapid diffusion of myosin and rapid unbinding of myosin from the actin network are stabilizing. We use numerical simulation to investigate travelling-wave solutions relevant to a steadily gliding cell and we consider a reduction of the model in which the cell adheres strongly to the substrate on which it is crawling. This work demonstrates that a number of existing models for the effect of myosin on cell motility can be understood as different sub-limits of our two-phase flow model.
A Dual-Stage Two-Phase Model of Selective Attention
ERIC Educational Resources Information Center
Hubner, Ronald; Steinhauser, Marco; Lehle, Carola
2010-01-01
The dual-stage two-phase (DSTP) model is introduced as a formal and general model of selective attention that includes both an early and a late stage of stimulus selection. Whereas at the early stage information is selected by perceptual filters whose selectivity is relatively limited, at the late stage stimuli are selected more efficiently on a…
23 CFR 636.202 - When are two-phase design-build selection procedures appropriate?
Code of Federal Regulations, 2010 CFR
2010-04-01
... 23 Highways 1 2010-04-01 2010-04-01 false When are two-phase design-build selection procedures appropriate? 636.202 Section 636.202 Highways FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION ENGINEERING AND TRAFFIC OPERATIONS DESIGN-BUILD CONTRACTING Selection Procedures, Award Criteria §...
Toward the use of similarity theory in two-phase choked flows
NASA Technical Reports Server (NTRS)
Hendericks, R. C.; Sengers, J. V.; Simoneau, R. J.
1980-01-01
Comparison of two phase choked flows in normalized coordinates were made between pure components and available data using a reference fluid to compute the thermophysical properties. The results are favorable. Solution of the governing equations for two LNG mixtures show some possible similarities between the normalized choked flows of the two mixtures, but the departures from the pure component loci are significant.
Toward the use of similarity theory in two-phase choked flows
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Simoneau, R. J.; Sengers, J. V.
1980-01-01
Comparison of two-phase choked flows in normalized coordinates were made between pure components and available data using a reference fluid to compute the thermophysical properties. The results are favorable. Solution of the governing equations for two LNG mixtures show some possible similarities between the normalized choked flows of the two mixtures, but the departures from the pure component locii are significant.
Three dimensional numerical prediction of two phase flow in industrial CFB boiler
Balzer, G.; Simonin, O.
1997-12-31
Gas-solid two phase flows are encountered in number of industrial applications such as pneumatic transport, catalytic cracking, coal combustors. The paper aims at presenting the numerical model of gas-solid flows which have been developed for several years at the Laboratoire National d`Hydraulique of Electricite de France and its application to the prediction of an industrial CFB Boiler.
Generating a Two-Phase Lesson for Guiding Beginners to Learn Basic Dance Movements
ERIC Educational Resources Information Center
Yang, Yang; Leung, Howard; Yue, Lihua; Deng, Liqun
2013-01-01
In this paper, an automated lesson generation system for guiding beginners to learn basic dance movements is proposed. It analyzes the dance to generate a two-phase lesson which can provide a suitable cognitive load thus offering an efficient learning experience. In the first phase, the dance is divided into small pieces which are patterns, and…
DNA-controlled partition of carbon nanotubes in polymer aqueous two-phase systems.
Ao, Geyou; Khripin, Constantine Y; Zheng, Ming
2014-07-23
Sorting single-wall carbon nanotubes (SWCNTs) of different chiralities is both scientifically interesting and technologically important. Recent studies have shown that polymer aqueous two-phase extraction is a very effective way to achieve nanotube sorting. However, works published to date have demonstrated only separation of surfactant-dispersed SWCNTs, and the mechanism of chirality-dependent SWCNT partition is not well understood. Here we report a systematic study of spontaneous partition of DNA-wrapped SWCNTs in several polymer aqueous two-phase systems. We show that partition of DNA-SWCNT hybrids in a given polymer two-phase system is strongly sequence-dependent and can be further modulated by salt and polymer additives. With the proper combination of DNA sequence, polymer two-phase system, and partition modulators, as many as 15 single-chirality nanotube species have been effectively purified from a synthetic mixture. As an attempt to provide a unified partition mechanism of SWCNTs dispersed by surfactants and by DNA, we present a qualitative analysis of solvation energy for SWCNT colloids in a polymer-modified aqueous phase. Our observation and analysis highlight the sensitive dependence of the hydration energy on the spatial distribution of hydrophilic functionalities.
Two parametric flow measurement in gas-liquid two-phase flow
NASA Astrophysics Data System (ADS)
Chen, Z.; Chen, C.; Xu, Y.; Zhao, Z.
The importance and current development of two parametric measurement during two-phase flow are briefly reviewed in this paper. Gas-liquid two-phase two parametric metering experiments were conducted by using an oval gear meter and a sharp edged orifice mounted in series in a horizontal pipe. Compressed air and water were used as gas and liquid phases respectively. The correlations, which can be used to predict the total flow rate and volumetric quality of two-phase flow or volumetric flow rate of each phase, have also been proposed in this paper. Comparison of the calculated values of flow rate of each phase from the correlations with the test data showed that the root mean square fractional deviation for gas flow rate is 2.9 percent and for liquid flow rate 4.4 percent. The method proposed in this paper can be used to measure the gas and liquid flow rate in two-phase flow region without having to separate the phases.
Phase distribution of nitrogen-water two-phase flow in parallel micro channels
NASA Astrophysics Data System (ADS)
Zhou, Mi; Wang, Shuangfeng; Zhou, You
2016-08-01
The present work experimentally investigated the phase splitting characteristics of gas-liquid two-phase flow passing through a horizontal-oriented micro-channel device with three parallel micro-channels. The hydraulic diameters of the header and the branch channels were 0.6 and 0.4 mm, respectively. Five different liquids, including de-ionized water and sodium dodecyl sulfate (SDS) solution with different concentration were employed. Different from water, the surface tension of SDS solution applied in this work decreased with the increment of mass concentration. Through series of visual experiments, it was found that the added SDS surfactant could obviously facilitate the two-phase flow through the parallel micro channels while SDS solution with low concentration would lead to an inevitable blockage of partial outlet branches. Experimental results revealed that the two phase distribution characteristics depended highly on the inlet flow patterns and the outlet branch numbers. To be specific, at the inlet of slug flow, a large amount of gas preferred flowing into the middle branch channel while the first branch was filled with liquid. However, when the inlet flow pattern was shifted to annular flow, all of the gas passed through the second and the last branches, with a little proportion of liquid flowing into the first channel. By comparison with the experimental results obtained from a microchannel device with five parallel micro-T channels, uneven distribution of the two phase can be markedly noticed in our present work.
23 CFR 636.202 - When are two-phase design-build selection procedures appropriate?
Code of Federal Regulations, 2011 CFR
2011-04-01
... 23 Highways 1 2011-04-01 2011-04-01 false When are two-phase design-build selection procedures appropriate? 636.202 Section 636.202 Highways FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION ENGINEERING AND TRAFFIC OPERATIONS DESIGN-BUILD CONTRACTING Selection Procedures, Award Criteria §...
Forced Two-Phase Helium Cooling Scheme for the Mu2e Transport Solenoid
Tatkowski, G.; Cheban, S.; Dhanaraj, N.; Evbota, D.; Lopes, M.; Nicol, T.; Sanders, R.; Schmitt, R.; Voirin, E.
2015-01-01
The Mu2e Transport Solenoid (TS) is an S-shaped magnet formed by two separate but similar magnets, TS-u and TS-d. Each magnet is quarter-toroid shaped with a centerline radius of approximately 3 m utilizing a helium cooling loop consisting of 25 to 27 horizontal-axis rings connected in series. This cooling loop configuration has been deemed adequate for cooling via forced single phase liquid helium; however it presents major challenges to forced two-phase flow such as “garden hose” pressure drop, concerns of flow separation from tube walls, difficulty of calculation, etc. Even with these disadvantages, forced two-phase flow has certain inherent advantages which make it a more attractive option than forced single phase flow. It is for this reason that the use of forced two-phase flow was studied for the TS magnets. This paper will describe the analysis using helium-specific pressure drop correlations, conservative engineering approach, helium properties calculated and updated at over fifty points, and how the results compared with those in literature. Based on the findings, the use of forced-two phase helium is determined to be feasible for steady-state cooling of the TS solenoids
Well logging interpretation of production profile in horizontal oil-water two phase flow pipes
NASA Astrophysics Data System (ADS)
Zhai, Lu-Sheng; Jin, Ning-De; Gao, Zhong-Ke; Zheng, Xi-Ke
2012-03-01
Due to the complicated distribution of local velocity and local phase hold up along the radial direction of pipe in horizontal oil-water two phase flow, it is difficult to measure the total flow rate and phase volume fraction. In this study, we carried out dynamic experiment in horizontal oil-water two phases flow simulation well by using combination measurement system including turbine flowmeter with petal type concentrating diverter, conductance sensor and flowpassing capacitance sensor. According to the response resolution ability of the conductance and capacitance sensor in different range of total flow rate and water-cut, we use drift flux model and statistical model to predict the partial phase flow rate, respectively. The results indicate that the variable coefficient drift flux model can self-adaptively tone the model parameter according to the oil-water two phase flow characteristic, and the prediction result of partial phase flow rate of oil-water two phase flow is of high accuracy.
COMPARING SIMULATED AND EXPERIMENTAL HYSTERETIC TWO- PHASE TRANSIENT FLUID FLOW PHENOMENA
A hysteretic model for two-phase permeability (k)-saturation (S)-pressure (P) relations is outlined that accounts for effects of nonwetting fluid entrapment. The model can be employed in unsaturated fluid flow computer codes to predict temporal and spatial fluid distributions. Co...
Multi-scale symbolic time reverse analysis of gas-liquid two-phase flow structures
NASA Astrophysics Data System (ADS)
Wang, Hongmei; Zhai, Lusheng; Jin, Ningde; Wang, Youchen
Gas-liquid two-phase flows are widely encountered in production processes of petroleum and chemical industry. Understanding the dynamic characteristics of multi-scale gas-liquid two-phase flow structures is of great significance for the optimization of production process and the measurement of flow parameters. In this paper, we propose a method of multi-scale symbolic time reverse (MSTR) analysis for gas-liquid two-phase flows. First, through extracting four time reverse asymmetry measures (TRAMs), i.e. Euclidean distance, difference entropy, percentage of constant words and percentage of reversible words, the time reverse asymmetry (TRA) behaviors of typical nonlinear systems are investigated from the perspective of multi-scale analysis, and the results show that the TRAMs are sensitive to the changing of dynamic characteristics underlying the complex nonlinear systems. Then, the MSTR analysis is used to study the conductance signals from gas-liquid two-phase flows. It is found that the multi-scale TRA analysis can effectively reveal the multi-scale structure characteristics and nonlinear evolution properties of the flow structures.
Implementation of the interfacial area transport equation in trace for boiling two-phase flows
NASA Astrophysics Data System (ADS)
Bernard, Matthew S.
Correctly predicting the interfacial area concentration (a i) is vital to the overall accuracy of the two-fluid model because ai describes the amount of surface area that exists between the two-phases, and is therefore directly related to interfacial mass, momentum and energy transfer. The conventional method for specifying ai in the two-fluid model is through flow regime-based empirical correlations coupled with regime transition criteria. However, a more physically consistent approach to predicting ai is through the interfacial area transport equation (IATE), which can address the deficiencies of the flow regime-based approach. Some previous studies have been performed to demonstrate the feasibility of IATE in developmental versions of the nuclear reactor systems analysis code, TRACE. However, a full TRACE version capable of predicting boiling two-phase flows with the IATE has not been established. Therefore, the current work develops a version of TRACE that is capable of predicting boiling two-phase flows using the IATE. The development is carried out in stages. First, a version of TRACE which employs the two-group IATE for adiabatic, vertical upward, air-water conditions is developed. An in-depth assessment on the existing experimental database is performed to select reliable experimental data for code assessment. Then, the implementation is assessed against the qualified air-water two-phase flow experimental data. Good agreement is observed between the experimental data for ai and the TRACE code with an average error of +/-9% for all conditions. Following the initial development, one-group IATE models for vertical downward and horizontal two-phase flows are implemented and assessed against qualified data. Finally, IATE models capable of predicting subcooled boiling two-phase flows are implemented. An assessment of the models shows that TRACE is capable of generating ai in subcooled boiling two-phase flows with the IATE and that heat transfer effects dominate
Study of Critical Heat Flux and Two-Phase Pressure Drop Under Reduced Gravity
NASA Technical Reports Server (NTRS)
Abdollahian, Davood; Quintal, Joseph; Barez, Fred; Zahm, Jennifer; Lohr, Victor
1996-01-01
The design of the two-phase flow systems which are anticipated to be utilized in future spacecraft thermal management systems requires a knowledge of two-phase flow and heat transfer phenomena in reduced gravities. This program was funded by NASA headquarters in response to NRA-91-OSSA-17 and was managed by Lewis Research Center. The main objective of this program was to design and construct a two-phase test loop, and perform a series of normal gravity and aircraft trajectory experiments to study the effect of gravity on the Critical Heat Flux (CHF) and onset of instability. The test loop was packaged on two aircraft racks and was also instrumented to generate data for two-phase pressure drop. The normal gravity tests were performed with vertical up and downflow configurations to bound the effect of gravity on the test parameters. One set of aircraft trajectory tests was performed aboard the NASA DC-9 aircraft. These tests were mainly intended to evaluate the test loop and its operational performance under actual reduced gravity conditions, and to produce preliminary data for the test parameters. The test results were used to demonstrate the applicability of the normal gravity models for prediction of the two-phase friction pressure drop. It was shown that the two-phase friction multipliers for vertical upflow and reduced gravity conditions can be successfully predicted by the appropriate normal gravity models. Limited critical heat flux data showed that the measured CHF under reduced gravities are of the same order of magnitude as the test results with vertical upflow configuration. A simplified correlation was only successful in predicting the measured CHF for low flow rates. Instability tests with vertical upflow showed that flow becomes unstable and critical heat flux occurs at smaller powers when a parallel flow path exists. However, downflow tests and a single reduced gravity instability experiment indicated that the system actually became more stable with a
Two-phase convective CO_{2} dissolution in saline aquifers
Martinez, Mario J.; Hesse, Marc A.
2016-01-30
Geologic carbon storage in deep saline aquifers is a promising technology for reducing anthropogenic emissions into the atmosphere. Dissolution of injected CO_{2} into resident brines is one of the primary trapping mechanisms generally considered necessary to provide long-term storage security. Given that diffusion of CO_{2} in brine is woefully slow, convective dissolution, driven by a small increase in brine density with CO_{2} saturation, is considered to be the primary mechanism of dissolution trapping. Previous studies of convective dissolution have typically only considered the convective process in the single-phase region below the capillary transition zone and have either ignored the overlying two-phase region where dissolution actually takes place or replaced it with a virtual region with reduced or enhanced constant permeability. Our objective is to improve estimates of the long-term dissolution flux of CO_{2} into brine by including the capillary transition zone in two-phase model simulations. In the fully two-phase model, there is a capillary transition zone above the brine-saturated region over which the brine saturation decreases with increasing elevation. Our two-phase simulations show that the dissolution flux obtained by assuming a brine-saturated, single-phase porous region with a closed upper boundary is recovered in the limit of vanishing entry pressure and capillary transition zone. For typical finite entry pressures and capillary transition zone, however, convection currents penetrate into the two-phase region. As a result, this removes the mass transfer limitation of the diffusive boundary layer and enhances the convective dissolution flux of CO_{2} more than 3 times above the rate assuming single-phase conditions.
Evaluation of the Sensitivity of Two-Phase Flow Model for the Steam Separator Analysis
Michio Murase; Masao Chaki
2006-07-01
Reducing of the pressure losses of steam separator systems of boiling water reactor (BWR) plants is useful to reduce the required pump head and enhance core stability design margin. The need to reduce the pressure losses of steam separator systems is especially important in BWR plants that have high power density cores and natural circulation systems. The core flow rate of a BWR plant with a natural circulation system is affected by the pressure losses of steam separator systems. In BWR plants with high power density cores, the core stability design margin is affected by these pressure losses. Generally, reducing the pressure losses of the steam separator systems leads to increased carry-under and carryover. Reducing the pressure losses while keeping the characteristics of both carry-under and carryover is desired, so many studies have been done. The steam separator of a BWR plant consists of a standpipe section, a swirl vane section and three-barrel sections. Two-phase flow of steam and water enters the steam separator through the standpipe section and reaches the swirl vane section. In the swirl vane section, the two-phase flow is given centrifugal force and is basically separated into steam and water. Therefore investigating the two-phase flow characteristics of the swirl vane section is very important. After the swirl vane section, the two-phase flow enters the barrel sections. Each barrel has a pick-off ring. The water in the barrel section is mainly removed by these pick-off rings because the water mainly flows upward as a liquid film in the barrel section due to the centrifugal force given in the swirl vane section. We researched the effect of using the drag force model of the swirling two-phase flow in analyzing a steam separator and we found that the drag force model greatly affects the results of the analysis. (authors)
Cryogenic two-phase flow and phase-change heat transfer in microgravity
NASA Astrophysics Data System (ADS)
Tai, Cheng-Feng
The applications of cryogenic flow and heat transfer are found in many different types of industries, whether it be the liquid fuel for propulsion or the cryogenic cooling in medical applications. It is very common to find the transportation of cryogenic flow under microgravity in space missions. For example, the liquid oxygen and hydrogen are used to power launch vehicles and helium is used for pressurizing the fuel tank. During the transportation process in pipes, because of high temperature and heat flux from the pipe wall, the cryogenic flow is always in a two-phase condition. As a result, the physics of cryogenic two-phase flow and heat transfer is an important topic for research. In this research, numerical simulation is employed to study fluid flow and heat transfer. The Sharp Interface Method (SIM) with a Cut-cell approach (SIMCC) is adopted to handle the two-phase flow and heat transfer computation. In SIMCC, the background grid is Cartesian and explicit true interfaces are immersed into the computational domain to divide the entire domain into different sub-domains/phases. In SIMCC, each phase comes with its own governing equations and the interfacial conditions act as the bridge to connect the information between the two phases. The Cut-cell approach is applied to handle nonrectangular cells cut by the interfaces and boundaries in SIMCC. With the Cut-cell approach, the conservative properties can be maintained better near the interface. This research will focus on developing the numerical techniques to simulate the two-phase flow and phase change phenomena for one of the major flow patterns in film boiling, the inverted annular flow.
Z-Estimation and Stratified Samples
Breslow, Norman E.; Hu, Jie; Wellner, Jon A.
2015-01-01
The infinite dimensional Z-estimation theorem offers a systematic approach to joint estimation of both Euclidean and non-Euclidean parameters in probabiity models for data. It is easily adapted for stratified sampling designs. This is important in applications to censored survival data because the inverse probability weights that modify the standard estimating equations often depend on the entire follow-up history. Since the weights are not predictable, they complicate the usual theory based on martingales. This paper considers joint estimation of regression coefficients and baseline hazard functions in the Cox proportional and Lin-Ying additive hazards models. Weighted likelihood equations are used for the former and weighted estimating equations for the latter. Regression coefficients and baseline hazards may be combined to estimate individual survival probabilities. Efficiency is improved by calibrating or estimating the weights using information available for all subjects. Although inefficient in comparison with likelihood inference for incomplete data, which is often difficult to implement, the approach provides consistent estimates of desired population parameters even under model misspecification. PMID:25588605
Acoustic propagation under tidally driven, stratified flow.
Finette, Steven; Oba, Roger; Shen, Colin; Evans, Thomas
2007-05-01
Amplitude and phase variability in acoustic fields are simulated within a canonical shelf-break ocean environment using sound speed distributions computed from hydrodynamics. The submesoscale description of the space and time varying environment is physically consistent with tidal forcing of stratified flows over variable bathymetry and includes the generation, evolution and propagation of internal tides and solibores. For selected time periods, two-dimensional acoustic transmission examples are presented for which signal gain degradation is computed between 200 and 500 Hz on vertical arrays positioned both on the shelf and beyond the shelf break. Decorrelation of the field is dominated by the phase contribution and occurs over 2-3 min, with significant recorrelation often noted for selected frequency subbands. Detection range is also determined in this frequency band. Azimuth-time variations in the acoustic field are illustrated for 100 Hz sources by extending the acoustic simulations to three spatial dimensions. The azimuthal and temporal structure of both the depth-averaged transmission loss and temporal correlation of the acoustic fields under different environmental conditions are considered. Depth-averaged transmission loss varies up to 4 dB, depending on a combination of source depth, location relative to the slope and tidally induced volumetric changes in the sound speed distribution.
Viscosity stratified fluids in turbulent channel flow
NASA Astrophysics Data System (ADS)
Soldati, Alfredo; Ahmadi, Somayeh; Roccon, Alessio; Zonta, Francesco
2016-11-01
Direct Numerical Simulation (DNS) is used to study the turbulent Poiseuille flow of two immiscible liquid layers inside a rectangular channel. A thin liquid layer (fluid 1) flows on top of a thick liquid layer (fluid 2), such that their thickness ratio is h1 /h2 = 1 / 9 . The two liquid layers have the same density but different viscosities (viscosity-stratified fluids). In particular, we consider three different values of the viscosity ratio λ =ν1 /ν2 : λ = 1 , λ = 0 . 875 and λ = 0 . 75 . Numerical Simulations are based on a Phase Field method to describe the interaction between the two liquid layers. Compared with the case of a single phase flow, the presence of a liquid-liquid interface produces a remarkable turbulence modulation inside the channel, since a significant proportion of the kinetic energy is subtracted from the mean flow and converted into work to deform the interface. This induces a strong turbulence reduction in the proximity of the interface and causes a substantial increase of the volume-flowrate. These effects become more pronounced with decreasing λ.
Lappe, R; Sant'anna, V; Brandelli, A
2012-01-01
Cerein 8A is an antimicrobial peptide with potential application against food spoilage and pathogenic bacteria. The partitioning of cerein 8A was investigated in two liquid-liquid extraction systems that are considered promising for bioseparation and purification purposes. Aqueous two-phase systems (ATPSs) were prepared with polyethylene glycol (PEG) and inorganic salts, and the addition of NaCl was investigated in this system. The best results concerning partition coefficients (K (b)) were obtained with PEG + ammonium sulphate, and K (b) value significantly increases when NaCl was added. Cerein 8A was effectively extracted into the micelle-rich phase in a 4% Triton X-114 medium. Recovery yield was higher for ATPS compared to micellar systems. Cerein 8A can be isolated from a crude suspension containing the bioactive molecule by ATPSs. Successful implementation of peptide partitioning represents an important step towards developing a low-cost effective separation method for cerein 8A.
Jet-mixing of initially-stratified liquid-liquid pipe flows: experiments and numerical simulations
NASA Astrophysics Data System (ADS)
Wright, Stuart; Ibarra-Hernandes, Roberto; Xie, Zhihua; Markides, Christos; Matar, Omar
2016-11-01
Low pipeline velocities lead to stratification and so-called 'phase slip' in horizontal liquid-liquid flows due to differences in liquid densities and viscosities. Stratified flows have no suitable single point for sampling, from which average phase properties (e.g. fractions) can be established. Inline mixing, achieved by static mixers or jets in cross-flow (JICF), is often used to overcome liquid-liquid stratification by establishing unstable two-phase dispersions for sampling. Achieving dispersions in liquid-liquid pipeline flows using JICF is the subject of this experimental and modelling work. The experimental facility involves a matched refractive index liquid-liquid-solid system, featuring an ETFE test section, and experimental liquids which are silicone oil and a 51-wt% glycerol solution. The matching then allows the dispersed fluid phase fractions and velocity fields to be established through advanced optical techniques, namely PLIF (for phase) and PTV or PIV (for velocity fields). CFD codes using the volume of a fluid (VOF) method are then used to demonstrate JICF breakup and dispersion in stratified pipeline flows. A number of simple jet configurations are described and their dispersion effectiveness is compared with the experimental results. Funding from Cameron for Ph.D. studentship (SW) gratefully acknowledged.
A two-phase solid/fluid model for dense granular flows including dilatancy effects
NASA Astrophysics Data System (ADS)
Mangeney, Anne; Bouchut, Francois; Fernandez-Nieto, Enrique; Koné, El-Hadj; Narbona-Reina, Gladys
2016-04-01
Describing grain/fluid interaction in debris flows models is still an open and challenging issue with key impact on hazard assessment [{Iverson et al.}, 2010]. We present here a two-phase two-thin-layer model for fluidized debris flows that takes into account dilatancy effects. It describes the velocity of both the solid and the fluid phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure [{Bouchut et al.}, 2016]. The model is derived from a 3D two-phase model proposed by {Jackson} [2000] based on the 4 equations of mass and momentum conservation within the two phases. This system has 5 unknowns: the solid and fluid velocities, the solid and fluid pressures and the solid volume fraction. As a result, an additional equation inside the mixture is necessary to close the system. Surprisingly, this issue is inadequately accounted for in the models that have been developed on the basis of Jackson's work [{Bouchut et al.}, 2015]. In particular, {Pitman and Le} [2005] replaced this closure simply by imposing an extra boundary condition at the surface of the flow. When making a shallow expansion, this condition can be considered as a closure condition. However, the corresponding model cannot account for a dissipative energy balance. We propose here an approach to correctly deal with the thermodynamics of Jackson's model by closing the mixture equations by a weak compressibility relation following {Roux and Radjai} [1998]. This relation implies that the occurrence of dilation or contraction of the granular material in the model depends on whether the solid volume fraction is respectively higher or lower than a critical value. When dilation occurs, the fluid is sucked into the granular material, the pore pressure decreases and the friction force on the granular phase increases. On the contrary, in the case of contraction, the fluid is expelled from the mixture, the pore pressure increases and the friction force diminishes. To
Damping and fluidelastic instability in two-phase cross-flow heat exchanger tube arrays
NASA Astrophysics Data System (ADS)
Moran, Joaquin E.
An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The model tube bundle had 10 cantilevered tubes in a parallel-triangular configuration, with a pitch ratio of 1.49. The two-phase flow loop used in this research utilized Refrigerant 11 as the working fluid, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of void fraction, density and velocity predictions. Three different damping measurement methodologies were implemented and compared in order to obtain a more reliable damping estimate. The methods were the traditionally used half-power bandwidth, the logarithmic decrement and an exponential fitting to the tube decay response. The decay trace was obtained by "plucking" the monitored tube from outside the test section using a novel technique, in which a pair of electromagnets changed their polarity at the natural frequency of the tube to produce resonance. The experiments showed that the half-power bandwidth produces higher damping values than the other two methods. The primary difference between the methods is caused by tube frequency shifting, triggered by fluctuations in the added mass and coupling between the tubes, which depend on void fraction and flow regime. The exponential fitting proved to be the more consistent and reliable approach to estimating damping. In order to examine the relationship between the damping ratio and mass flux, the former was plotted as a function of void fraction and pitch mass flux in an iso-contour plot. The results showed that damping is not independent of mass
Analysis of Two-Phase Flow in Damper Seals for Cryogenic Turbopumps
NASA Technical Reports Server (NTRS)
Arauz, Grigory L.; SanAndres, Luis
1996-01-01
Cryogenic damper seals operating close to the liquid-vapor region (near the critical point or slightly su-cooled) are likely to present two-phase flow conditions. Under single phase flow conditions the mechanical energy conveyed to the fluid increases its temperature and causes a phase change when the fluid temperature reaches the saturation value. A bulk-flow analysis for the prediction of the dynamic force response of damper seals operating under two-phase conditions is presented as: all-liquid, liquid-vapor, and all-vapor, i.e. a 'continuous vaporization' model. The two phase region is considered as a homogeneous saturated mixture in thermodynamic equilibrium. Th flow in each region is described by continuity, momentum and energy transport equations. The interdependency of fluid temperatures and pressure in the two-phase region (saturated mixture) does not allow the use of an energy equation in terms of fluid temperature. Instead, the energy transport is expressed in terms of fluid enthalpy. Temperature in the single phase regions, or mixture composition in the two phase region are determined based on the fluid enthalpy. The flow is also regarded as adiabatic since the large axial velocities typical of the seal application determine small levels of heat conduction to the walls as compared to the heat carried by fluid advection. Static and dynamic force characteristics for the seal are obtained from a perturbation analysis of the governing equations. The solution expressed in terms of zeroth and first order fields provide the static (leakage, torque, velocity, pressure, temperature, and mixture composition fields) and dynamic (rotordynamic force coefficients) seal parameters. Theoretical predictions show good agreement with experimental leakage pressure profiles, available from a Nitrogen at cryogenic temperatures. Force coefficient predictions for two phase flow conditions show significant fluid compressibility effects, particularly for mixtures with low mass
Interfacial area transport for reduced-gravity two-phase flows
NASA Astrophysics Data System (ADS)
Vasavada, Shilp
An extensive experimental and theoretical study of two-phase flow behavior in reduced-gravity conditions has been performed as part of the current research and the results of the same are presented in this thesis. The research was undertaken to understand the behavior of two-phase flows in an environment where the gravity field is reduced as compared to that on earth. The goal of the study was to develop a model capable of predicting the flow behavior. An experimental program was developed and accomplished which simulated reduced-gravity conditions on earth by using two liquids of similar density, thereby decreasing the body force effect akin to actual reduced-gravity conditions. The justification and validation of this approach has been provided based on physical arguments as well as comparison of acquired data with that obtained aboard parabolic flights by previous researchers. The experimental program produced an extensive dataset of local and averaged two-phase flow parameters using state-of-the-art instrumentation. Such data were acquired for a wide range of flow conditions at different radial and axial locations in a 25 mm inner diameter test facility. The current dataset is, in the author's opinion, the most extensive and detailed dataset available for such conditions at present. Analysis of the data revealed important differences between two-phase flows in normal and reduced-gravity conditions. The data analysis also highlighted key interaction mechanisms between the fluid particles and physical phenomena occurring in two-phase flows under reduced-gravity conditions. The interfacial area transport equation (IATE) for reduced-gravity conditions has been developed by considering two groups of bubbles/drops and mechanistically modeling the interaction mechanisms. The developed model has been benchmarked against the acquired data and the predictions of the model compared favorably against the experimental data. This signifies the success achieved in modeling
STRATIFIED COMPOSITION EFFECTS ON PLANETARY NEUTRON FLUX
O. GASNAULT; ET AL
2001-01-01
All the bodies of the solar system that are directly irradiated by the galactic cosmic rays, emit enough neutrons to allow a measurement from space. These leakage neutron fluxes are indexes of the surface composition, depending on the energy of the neutrons [1]. Recent work propose geochemical interpretations of these fluxes: the thermal energy range is sensitive to iron, titanium, rare earth elements and thorium [2, 3], the epithermal energy range is sensitive to hydrogen, samarium and gadolinium [2] and the fast energy range is representative of the average soil atomic mass [4]. Nevertheless these studies make the hypothesis of a composition uniform within the footprint of the spectrometer and independent of depth. We show in this abstract that a stratified composition could change significantly the flux intensity and complicate the interpretation of the measurements. The neutron leakage flux is a competition between production effects (sensitive at high energy) and diffusion-capture effects (mostly sensitive at low energy). On one hand, it happens to be that the elements which produce the higher number of neutrons in typical lunar compositions are iron and titanium, which have also large cross section of absorption with the neutrons. On the other hand, the maximum of neutron intensity does not occur at the surface but at about 180 g cm{sup {minus}2} in depth. Therefore, if we have an iron- and/or titanium-rich soil (important production of neutrons) with a top layer having less iron and/or titanium (i.e. more transparent to the neutrons), we can expect an enhancement of the flux compared to a uniform composition.
Stratified composition effects on planetary neutron flux
NASA Astrophysics Data System (ADS)
Gasnault, O.
2001-01-01
All the bodies of the solar system that are directly irradiated by the galactic cosmic rays, emit enough neutrons to allow a measurement from space. These leakage neutron fluxes are indexes of the surface composition, depending on the energy of the neutrons (1). Recent work propose geochemical interpretations of these fluxes: the thermal energy range is sensitive to iron, titanium, rare earth elements and thorium (2, 3), the epithermal energy range is sensitive to hydrogen, samarium and gadolinium (2) and the fast energy range is representative of the average soil atomic mass (4). Nevertheless these studies make the hypothesis of a composition uniform within the footprint of the spectrometer and independent of depth. We show in this abstract that a stratified composition could change significantly the flux intensity and complicate the interpretation of the measurements. The neutron leakage flux is a competition between production effects (sensitive at high energy) and diffusion-capture effects (mostly sensitive at low energy). On one hand, it happens to be that the elements which produce the higher number of neutrons in typical lunar compositions are iron and titanium, which have also large cross section of absorption with the neutrons. On the other hand, the maximum of neutron intensity does not occur at the surface but at about 180 g cm(sup (minus)2) in depth. Therefore, if we have an iron- and/or titanium-rich soil (important production of neutrons) with a top layer having less iron and/or titanium (i.e. more transparent to the neutrons), we can expect an enhancement of the flux compared to a uniform composition.
Measurement of Two-Phase Flow Fields by Application of Dynamic Electrical Impedance Imaging
Kim, KyungYoun; Kang, Sook In; Kim, Ho Chan; Kim, Sin; Lee, Yoon Joon; Kim, Min Chan; Anghaie, Samim
2002-07-01
This study presents a visualization technique for the phase distribution in a two-phase flow field with an electrical impedance imaging technique, which reconstructs the resistivity distribution with electrical responses that are determined by corresponding excitations. Special emphasis is placed on the development of dynamic imaging technique for two-phase system undergoing a rapid transient, which could not be visualized with conventional static imaging techniques. The proposed algorithm treats the image reconstruction problem as a nonlinear state estimation problem and the unknown state (resistivity distribution, i.e. phase distribution) is estimated with the aid of a Kalman filter in a minimum mean square error sense. Several illustrative examples with computer simulations are successfully provided to verify the reconstruction performance of the proposed algorithm. (authors)
Static and dynamic strain aging in two-phase {gamma}-titanium aluminides
Christoph, U.; Appel, F.; Wagner, R.
1997-12-31
Deformation of two-phase titanium aluminides exhibits discontinuous yielding and a negative strain rate sensitivity over the temperature range 450--750 K. These phenomena are usually associated with the Portevin-LeChatelier effect which is due to the dynamic interaction of diffusing defects with the dislocations. The resulting glide resistance was investigated by static strain aging. The experiments involve the prestraining of samples followed by aging under a relaxing load for certain periods of time. Reloading of the samples resulted in distinct yield points. The investigations were performed on two-phase {gamma}-titanium aluminides having different compositions and microstructures which are currently being considered for technical applications. Accordingly, dislocation locking occurs with fast kinetics which is characterized by a low activation energy. The experimental results will be discussed with respect to the nature of the diffusional mechanism and possible implication on the mechanical properties of the materials.
Performance of WPA Conductivity Sensor during Two-Phase Fluid Flow in Microgravity
NASA Technical Reports Server (NTRS)
Carter, Layne; O'Connor, Edward W.; Snowdon, Doug
2003-01-01
The Conductivity Sensor designed for use in the Node 3 Water Processor Assembly (WPA) was based on the existing Space Shuttle application for the fuel cell water system. However, engineering analysis has determined that this sensor design is potentially sensitive to two-phase fluid flow (gadliquid) in microgravity. The source for this sensitivity is the fact that gas bubbles will become lodged between the sensor probe and the wall of the housing without the aid of buoyancy in l-g. Once gas becomes lodged in the housing, the measured conductivity will be offset based on the volume of occluded gas. A development conductivity sensor was flown on the NASA Microgravity Plan to measure the offset, which was determined to range between 0 and 50%. Based on these findings, a development program was initiated at the sensor s manufacturer to develop a sensor design fully compatible with two-phase fluid flow in microgravity.
Interfacial structures of confined air-water two-phase bubbly flow
Kim, S.; Ishii, M.; Wu, Q.; McCreary, D.; Beus, S.G.
2000-08-01
The interfacial structure of the two-phase flows is of great importance in view of theoretical modeling and practical applications. In the present study, the focus is made on obtaining detailed local two-phase parameters in the air-water bubbly flow in a rectangular vertical duct using the double-sensor conductivity probe. The characteristic wall-peak is observed in the profiles of the interracial area concentration and the void fraction. The development of the interfacial area concentration along the axial direction of the flow is studied in view of the interfacial area transport and bubble interactions. The experimental data is compared with the drift flux model with C{sub 0} = 1.35.
Use of two-phase flow heat transfer method in spacecraft thermal system
NASA Technical Reports Server (NTRS)
Hye, A.
1985-01-01
In space applications, weight, volume and power are critical parameters. Presently liquid freon is used in the radiator planels of the Space Shuttle to dissipate heat. This requires a large amount of freon, large power for pumps, large volume and weight. Use of two-phase flow method to transfer heat can reduce them significantly. A modified commercial vapor compression refrigerator/freezer was sucessfully flown in STS-4 to study the effect of zero-gravity on the system. The duty cycle was about 5 percent higher in flight as compared to that on earth due to low flow velocity in condenser. The vapor Reynolds number at exit was about 4000 as compared to about 12,000. Efforts are underway to design a refrigerator/freezer using an oil-free compressor for Spacelab Mission 4 scheduled to fly in January 1986. A thermal system can be designed for spacecraft using the two-phase flow to transfer heat economically.
An improved stochastic separated flow model for turbulent two-phase flow
NASA Astrophysics Data System (ADS)
Chan, C. K.; Zhang, H. Q.; Lau, K. S.
An improved stochastic separated flow model is proposed to obtain reasonable statistical characteristics of a two-phase flow. Effects of the history of a particle and its current trajectory position on the mean-square fluctuating velocity of the dispersed phase are continuously considered in this model. Comparing with the conventional model, results using the improved model are more reasonable and can also be obtained more easily. Furthermore, the improved model requires less computational particles for simulating dispersed-phase turbulence at the beginning of the stochastic trajectory. In this paper, an application in turbulent two-phase flow of planar mixing layer is carried out. Numerical results including velocity, mean-square fluctuating velocity, particle number density and pdf of fluctuation velocity of dispersed phase are shown to compare well with experimental data.
On the Shape Sensitivity of the First Dirichlet Eigenvalue for Two-Phase Problems
Dambrine, M.; Kateb, D.
2011-02-15
We consider a two-phase problem in thermal conductivity: inclusions filled with a material of conductivity {sigma}{sub 1} are layered in a body of conductivity {sigma}{sub 2}. We address the shape sensitivity of the first eigenvalue associated with Dirichlet boundary conditions when both the boundaries of the inclusions and the body can be modified. We prove a differentiability result and provide the expressions of the first and second order derivatives. We apply the results to the optimal design of an insulated body. We prove the stability of the optimal design thanks to a second order analysis. We also continue the study of an extremal eigenvalue problem for a two-phase conductor in a ball initiated by Conca et al. (Appl. Math. Optim. 60(2):173-184, 2009) and pursued in Conca et al. (CANUM 2008, ESAIM Proc., vol. 27, pp. 311-321, EDP Sci., Les Ulis, 2009).
Decay of the 3D inviscid liquid-gas two-phase flow model
NASA Astrophysics Data System (ADS)
Zhang, Yinghui
2016-06-01
We establish the optimal {Lp-L2(1 ≤ p < 6/5)} time decay rates of the solution to the Cauchy problem for the 3D inviscid liquid-gas two-phase flow model and analyze the influences of the damping on the qualitative behaviors of solution. Compared with the viscous liquid-gas two-phase flow model (Zhang and Zhu in J Differ Equ 258:2315-2338, 2015), our results imply that the friction effect of the damping is stronger than the dissipation effect of the viscosities and enhances the decay rate of the velocity. Our proof is based on Hodge decomposition technique, the {Lp-L2} estimates for the linearized equations and an elaborate energy method.
Some issues in the simulation of two-phase flows: The relative velocity
NASA Astrophysics Data System (ADS)
Gräbel, J.; Hensel, S.; Ueberholz, P.; Zeidan, D.; Farber, P.
2016-06-01
In this paper we compare numerical approximations for solving the Riemann problem for a hyperbolic two-phase flow model in two-dimensional space. The model is based on mixture parameters of state where the relative velocity between the two-phase systems is taken into account. This relative velocity appears as a main discontinuous flow variable through the complete wave structure and cannot be recovered correctly by some numerical techniques when simulating the associated Riemann problem. Simulations are validated by comparing the results of the numerical calculation qualitatively with OpenFOAM software. Simulations also indicate that OpenFOAM is unable to resolve the relative velocity associated with the Riemann problem.
Two-phase velocity measurements around cylinders using particle image velocimetry
Hassan, Y.A.; Philip, O.G.; Schmidl, W.D.
1995-09-01
The particle Image Velocimetry flow measurement technique was used to study both single-phase flow and two-phase flow across a cylindrical rod inserted in a channel. First, a flow consisting of only a single-phase fluid was studied. The experiment consisted of running a laminar flow over four rods inserted in a channel. The water flow rate was 126 cm{sup 3}/s. Then a two-phase flow was studied. A mixture of water and small air bubbles was used. The water flow rate was 378 cm{sup 3}/s and the air flow rate was approximately 30 cm{sup 3}/s. The data are analyzed to obtain the velocity fields for both experiments. After interpretation of the velocity data, forces acting on a bubble entrained by the vortex were calculated successfully. The lift and drag coefficients were calculated using the velocity measurements and the force data.
An acoustic-convective splitting-based approach for the Kapila two-phase flow model
NASA Astrophysics Data System (ADS)
ten Eikelder, M. F. P.; Daude, F.; Koren, B.; Tijsseling, A. S.
2017-02-01
In this paper we propose a new acoustic-convective splitting-based numerical scheme for the Kapila five-equation two-phase flow model. The splitting operator decouples the acoustic waves and convective waves. The resulting two submodels are alternately numerically solved to approximate the solution of the entire model. The Lagrangian form of the acoustic submodel is numerically solved using an HLLC-type Riemann solver whereas the convective part is approximated with an upwind scheme. The result is a simple method which allows for a general equation of state. Numerical computations are performed for standard two-phase shock tube problems. A comparison is made with a non-splitting approach. The results are in good agreement with reference results and exact solutions.
Two-phase flow patterns in adiabatic and diabatic corrugated plate gaps
NASA Astrophysics Data System (ADS)
Polzin, A.-E.; Kabelac, S.; de Vries, B.
2016-09-01
Correlations for two-phase heat transfer and pressure drop can be improved considerably, when they are adapted to specific flow patterns. As plate heat exchangers find increasing application as evaporators and condensers, there is a need for flow pattern maps for corrugated plate gaps. This contribution presents experimental results on flow pattern investigations for such a plate heat exchanger background, using an adiabatic visualisation setup as well as a diabatic setup. Three characteristic flow patterns were observed in the considered range of two-phase flow: bubbly flow, film flow and slug flow. The occurrence of these flow patterns is a function of mass flux, void fraction, fluid properties and plate geometry. Two different plate geometries having a corrugation angle of 27° and 63°, respectively and two different fluids (water/air and R365mfc liquid/vapor) have been analysed. A flow pattern map using the momentum flux is presented.
NASA Astrophysics Data System (ADS)
Bondar, A.; Buzulutskov, A.; Dolgov, A.; Nosov, V.; Shekhtman, L.; Shemyakina, E.; Sokolov, A.
2017-02-01
A two-phase Cryogenic Avalanche Detector (CRAD) with electroluminescence (EL) gap, operated in argon doped with a minor (49±7 ppm) admixture of nitrogen, has been studied. The EL gap was optically read out using cryogenic PMTs located on the perimeter of the gap. We present the results of the measurements of the N2 content, detector sensitivity to X-ray-induced signals, EL gap yield and electron lifetime in the liquid. The detector sensitivity, at a drift field in liquid Ar of 0.6 kV/cm, was measured to be 9 and 16 photoelectrons recorded at the PMTs per keV of deposited energy at 23 and 88 keV respectively. Such two-phase detectors, with enhanced sensitivity to the S2 (ionization-induced) signal, are relevant in the field of argon detectors for dark matter search and low energy neutrino detection.
A modified homogeneous relaxation model for CO2 two-phase flow in vapour ejector
NASA Astrophysics Data System (ADS)
Haida, M.; Palacz, M.; Smolka, J.; Nowak, A. J.; Hafner, A.; Banasiak, K.
2016-09-01
In this study, the homogenous relaxation model (HRM) for CO2 flow in a two-phase ejector was modified in order to increase the accuracy of the numerical simulations The two- phase flow model was implemented on the effective computational tool called ejectorPL for fully automated and systematic computations of various ejector shapes and operating conditions. The modification of the HRM was performed by a change of the relaxation time and the constants included in the relaxation time equation based on the experimental result under the operating conditions typical for the supermarket refrigeration system. The modified HRM was compared to the HEM results, which were performed based on the comparison of motive nozzle and suction nozzle mass flow rates.
Thermal and dynamical regimes of single- and two-phase magmatic flow in dikes
NASA Technical Reports Server (NTRS)
Carrigan, Charles R.; Schubert, Gerald; Eichelberger, John C.
1992-01-01
The coupling between thermal and dynamical regimes of single- and two-phase magmatic flow in dikes, due to temperature-dependent viscosity and dissipation, was investigated using finite element calculations of magma flow in dikelike channels with length-to-width ratios of 1000:1 or more. Solutions of the steady state equations governing magma flow are obtained for a variety of conditions ranging from idealized plane-parallel models to cases involving nonparallel geometry and two-phase flows. The implications of the numerical simulations for the dynamics of flow in a dike-reservoir system and the consequences of dike entrance conditions on magmatic storage are discussed. Consideration is also given to an unmixing/self-lubrication mechanism which may be important for the lubrication of silicic magmas rising to the earth's surface in mixed magma ascent scenarios, which naturally segregates magma mixtures of two components with differing viscosities to minimize the driving pressure gradient.
Parallel phase-shifting color digital holography using two phase shifts.
Kakue, Takashi; Tahara, Tatsuki; Ito, Kenichi; Shimozato, Yuki; Awatsuji, Yasuhiro; Nishio, Kenzo; Ura, Shogo; Kubota, Toshihiro; Matoba, Osamu
2009-12-01
We propose parallel phase-shifting color digital holography using two phase shifts. This technique enables the instantaneous acquisition of three-dimensional information of a moving color object. The interference fringe image that contains six holograms with two phase shifts for three wavelengths is recorded by a single shot exposure. Decreasing the degree of space-division multiplexing of these holograms makes it possible to suppress the degradation of the image quality owing to the aliasing caused by the multiplexing. Numerical simulation and preliminary experiments demonstrate the validity of the proposed technique; the reconstructed images of the proposed technique are clearer than those of the previously reported single-shot phase-shifting color digital holography that uses four phase steps.
Thermal test results of the two-phase thermal bus technology demonstration loop
NASA Technical Reports Server (NTRS)
Edelstein, Fred; Liandris, Maria; Rankin, J. Gary
1987-01-01
A two-phase heat transport system, the Thermal Bus Technology Demonstrator, has been built and tested for NASA Johnson Space Center for application on Space Station. The loop is a separated two-phase system that uses evaporator flow control valves and liquid condenser flooding to achieve temperature control. Both ambient and thermal vacuum tests have been completed in NASA's Chamber A, initially using Freon-11 and then ammonia as the working fluid. Overall, the tests were quite successful, with the bus achieving all major test objectives, including operation at 19.5 kW and set points at 35 F (1.7 C), 70 F (21.1 C) and 104 F (40.0 C), load sharing, asymmetrical heating and isothermality around the loop. Low plate to vapor temperature drops were obtained for the monogroove cold plate using ammonia and are indicative of the high evaporative film coefficients obtainable with this design.
Not Available
1991-07-01
The possible head degradation of the SRPR pumps may be attributable to two independent phenomena, one due to the inception of cavitation and the other due to the two-phase flow phenomena. The head degradation due to the appearance of cavitation on the pump blade is hardly likely in the conventional pressurized water reactor (PWR) since the coolant circulating line is highly pressurized so that the cavitation is difficult to occur even at LOCA (loss of coolant accident) conditions. On the other hand, the suction pressure of SRPR pump is order-of-magnitude smaller than that of PWR so that the cavitation phenomena, may prevail, should LOCA occur, depending on the extent of LOCA condition. In this study, therefore, both cavitation phenomena and two-phase flow phenomena were investigated for the SRPR pump by using various analytical tools and the numerical results are presented herein.
Computer code for gas-liquid two-phase vortex motions: GLVM
NASA Technical Reports Server (NTRS)
Yeh, T. T.
1986-01-01
A computer program aimed at the phase separation between gas and liquid at zero gravity, induced by vortex motion, is developed. It utilizes an explicit solution method for a set of equations describing rotating gas-liquid flows. The vortex motion is established by a tangential fluid injection. A Lax-Wendroff two-step (McCormack's) numerical scheme is used. The program can be used to study the fluid dynamical behavior of the rotational two-phase fluids in a cylindrical tank. It provides a quick/easy sensitivity test on various parameters and thus provides the guidance for the design and use of actual physical systems for handling two-phase fluids.
Measurement of average density and relative volumes in a dispersed two-phase fluid
Sreepada, Sastry R.; Rippel, Robert R.
1992-01-01
An apparatus and a method are disclosed for measuring the average density and relative volumes in an essentially transparent, dispersed two-phase fluid. A laser beam with a diameter no greater than 1% of the diameter of the bubbles, droplets, or particles of the dispersed phase is directed onto a diffraction grating. A single-order component of the diffracted beam is directed through the two-phase fluid and its refraction is measured. Preferably, the refracted beam exiting the fluid is incident upon a optical filter with linearly varing optical density and the intensity of the filtered beam is measured. The invention can be combined with other laser-based measurement systems, e.g., laser doppler anemometry.
Performance Prediction of Two-Phase Geothermal Reservoir using Lumped Parameter Model
NASA Astrophysics Data System (ADS)
Nurlaela, F.; Sutopo
2016-09-01
Many studies have been conducted to simulate performance of low-temperature geothermal reservoirs using lumped parameter method. Limited work had been done on applying non-isothermal lumped parameter models to higher temperature geothermal reservoirs. In this study, the lumped parameter method was applied to high-temperature two phase geothermal reservoirs. The model couples both energy and mass balance equations thus can predict temperature, pressure and fluid saturation changes in the reservoir as a result of production, reinjection of water, and/or natural recharge. This method was validated using reservoir simulation results of TOUGH2. As the results, the two phase lumped parameter model simulation without recharge shows good matching, however reservoir model with recharge condition show quite good conformity.
Workshop on Two-Phase Fluid Behavior in a Space Environment
NASA Astrophysics Data System (ADS)
Swanson, Theodore D.; Juhasz, Al; Long, W. Russ; Ottenstein, Laura
The Workshop was successful in achieving its main objective of identifying a large number of technical issues relating to the design of two-phase systems for space applications. The principal concern expressed was the need for verified analytical tools that will allow an engineer to confidently design a system to a known degree of accuracy. New and improved materials, for such applications as thermal storage and as heat transfer fluids, were also identified as major needs. In addition to these research efforts, a number of specific hardware needs were identified which will require development. These include heat pumps, low weight radiators, advanced heat pipes, stability enhancement devices, high heat flux evaporators, and liquid/vapor separators. Also identified was the need for a centralized source of reliable, up-to-date information on two-phase flow in a space environment.
Design and test of a pumped two-phase mounting plate. [for spacecraft thermal control systems
NASA Technical Reports Server (NTRS)
Grote, M. G.; Swanson, T. D.
1985-01-01
The design, fabrication, and testing of the full-scale development unit of a pumped two-phase mounting plate (TPMP) used in advanced two-phase spacecraft thermal control systems are described. The mounting plate is tested with R-11 in the evaporator mode for total heat loads of over 3000 watts and local heat fluxes over 4 W/sq cm, and in the condenser mode with condenser loads from 60 to 400 watts and inlet qualities from 8 to 94 percent. The calculated heat-transfer coefficients are between 0.66 and 1.0 W/sq cm/C and are nearly independent of the flow rate and heat load except at very low heat loads. It is shown that the TPMP can be run with inlet conditions down to 22 C subcooling without any significant gradients in the plate and that it performs well with nonuniform heat fluxes.
Microstructures and Mechanical Properties of Two-Phase Alloys Based on NbCr(2)
Cady, C.M.; Chen, K.C.; Kotula, P.G.; Mauro, M.E.; Thoma, D.J.
1998-12-07
A two-phase, Nb-Cr-Ti alloy (bee+ C15 Laves phase) has been developed using several alloy design methodologies. In effort to understand processing-microstructure-property relationships, diffment processing routes were employed. The resulting microstructure and mechanical properties are discussed and compared. Plasma arc-melted samples served to establish baseline, . . . as-cast properties. In addition, a novel processing technique, involving decomposition of a supersaturated and metastable precursor phase during hot isostatic pressing (HIP), was used to produce a refined, equilibrium two-phase microstructure. Quasi-static compression tests as a ~ function of temperature were performed on both alloy types. Different deformation mechanisms were encountered based upon temperature and microstructure.
Evaporation on/in Capillary Structures of High Heat Flux Two-Phase Devices
NASA Technical Reports Server (NTRS)
Faghri, Amir; Khrustalev, Dmitry
1996-01-01
Two-phase devices (heat pipes, capillary pumped loops, loop heat pipes, and evaporators) have become recognized as key elements in thermal control systems of space platforms. Capillary and porous structures are necessary and widely used in these devices, especially in high heat flux and zero-g applications, to provide fluid transport and enhanced heat transfer during vaporization and condensation. However, some unexpected critical phenomena, such as dryout in long heat pipe evaporators and high thermal resistance of loop heat pipe evaporators with high heat fluxes, are possible and have been encountered in the use of two-phase devices in the low gravity environment. Therefore, a detailed fundamental investigation is proposed to better understand the fluid behavior in capillary-porous structures during vaporization at high heat fluxes. The present paper addresses some theoretical aspects of this investigation.
Nonequilibrium hydrogen combustion in one- and two-phase supersonic flow
Chang, H.T.; Hourng, L.W.; Chien, L.C.
1997-05-01
A time-splitting method for the numerical simulation of stiff nonequilibrium combustion problem was developed. The algorithm has been applied to simulate the shock-induced combustion and to investigate a supersonic one-and two-phase flowfield. The results are physically reasonable and demonstrate that the presence of particles has a dramatic effect on the nozzle flowfield and the thrust. Supersonic combustion usually happens in high speed flying aerodynamic problems, such as supersonic combustion ramjet (scramjet) engine for hypersonic airbreathing vehicles. Particularly for the scramjet engine, due to short residence time in the combustion chamber, it still contains incomplete combustion fuel as it enters the nozzle. For solid propellant rocket motors, the exhaust stream contains particles of aluminum oxide. In these two-phase nozzle flows, transfer of momentum and heat between gas particles often result in a decrease of nozzle efficiency.
Membrane-less micro fuel cell based on two-phase flow
NASA Astrophysics Data System (ADS)
Hashemi, S. M. H.; Neuenschwander, M.; Hadikhani, P.; Modestino, M. A.; Psaltis, D.
2017-04-01
Most microfluidic fuel cells use highly soluble fuels and oxidants in streams of liquid electrolytes to overcome the mass transport limitations that result from the low solubility of gaseous reactants such as hydrogen and oxygen. In this work, we address these limitations by implementing controlled two-phase flows of these gases in a set of microchannels electrolytically connected through a narrow gap. Annular flows of the gases reshape the concentration boundary layer over the surface of electrodes and increase the mass-transport limited current density in the system. Our results show that the power density of a two-phase system with hydrogen and oxygen streams is an order of magnitude higher than that of single phase system consisting of liquid electrolytes saturated with the same reactants. The reactor design described here can be employed to boost the performance of MFFCs and put them in a more competitive position compared to membrane based fuel cells.
A continuum theory for two-phase flows of particulate solids: application to Poiseuille flows
NASA Astrophysics Data System (ADS)
Monsorno, Davide; Varsakelis, Christos; Papalexandris, Miltiadis V.
2015-11-01
In the first part of this talk, we present a novel two-phase continuum model for incompressible fluid-saturated granular flows. The model accounts for both compaction and shear-induced dilatancy and accommodates correlations for the granular rheology in a thermodynamically consistent way. In the second part of this talk, we exercise this two-phase model in the numerical simulation of a fully-developed Poiseuille flow of a dense suspension. The numerical predictions are shown to compare favorably against experimental measurements and confirm that the model can capture the important characteristics of the flow field, such as segregation and formation of plug zones. Finally, results from parametric studies with respect to the initial concentration, the magnitude of the external forcing and the width of the channel are presented and the role of these physical parameters is quantified. Financial Support has been provided by SEDITRANS, an Initial Training Network of the European Commission's 7th Framework Programme
Targeted delivery by smart capsules for controlling two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Fan, Jing; Abbaspourrad, Alireza; Weitz, David; Harvard Weitzgroup Team
2015-11-01
Two-phase flow in porous media is significantly influenced by the physical properties of the fluids and the geometry of the medium. We develop a variety of smart microcapsules that can deliver and release specific substances to the target location in the porous medium, and therefore change the fluid property or medium geometry at certain locations. In this talk, I will present two types of smart capsules for targeted surfactant delivery to the vicinity of oil-water interface and targeted microgel delivery for improving the homogeneity of the porous medium, respectively. We further prove the concept by monitoring the capsule location and the fluid structure in the porous media by micro-CT and confocal microscopy. This technique not only is of particular importance to the relevant industry applications especially in the oil industry but also opens a new window to study the mechanism of two-phase flow in porous media. Advanced Energy Consortium BEG08-027.
Two phase choke flow in tubes with very large L/D
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Simoneau, R. J.
1977-01-01
Data were obtained for two phase and gaseous choked flow nitrogen in a long constant area duct of 16200 L/D with a diverging diffuser attached to the exit. Flow rate data were taken along five isotherms (reduced temperature of 0.81, 0.96, 1.06, 1.12, and 2.34) for reduced pressures to 3. The flow rate data were mapped in the usual manner using stagnation conditions at the inlet mixing chamber upstream of the entrance length. The results are predictable by a two phase homogeneous equilibrium choking flow model which includes wall friction. A simplified theory which in essence decouples the long tube region from the high acceleration choking region also appears to predict the data resonably well, but about 15 percent low.
Construction of Representative Pore Morphologies in Disordered Nanoporous Two-Phase Materials
Toney, Michael F
2003-04-01
Materials with nanometer size heterogeneities are commonplace in the physical and biological sciences and often exhibit complex morphologies. Although this morphology has a dramatic effect on the materials' properties (e.g., transport and reaction processes), it is often difficult to accurately characterize. We describe a method, using a novel analysis of small angle x-ray scattering data, of generating representative three-dimensional morphologies of isotropic two-phase materials (one class of heterogeneous materials) where the morphology is disordered. This is applied to thin films containing nanometer sized pores with a range of porosities (4-44%). These representations provide a visualization of the pore morphology, give the pore size scale and extent of interconnection, and permit the determination of the transitions from closed pore to interconnected pores to bicontinuous morphology. This methodology will be valuable for characterizing two-phase systems, such as polymer blends, microemulsions, porous geological materials, bones, cements and ceramics.
Workshop on Two-Phase Fluid Behavior in a Space Environment
NASA Technical Reports Server (NTRS)
Swanson, Theodore D. (Editor); Juhasz, AL (Editor); Long, W. Russ (Editor); Ottenstein, Laura (Editor)
1989-01-01
The Workshop was successful in achieving its main objective of identifying a large number of technical issues relating to the design of two-phase systems for space applications. The principal concern expressed was the need for verified analytical tools that will allow an engineer to confidently design a system to a known degree of accuracy. New and improved materials, for such applications as thermal storage and as heat transfer fluids, were also identified as major needs. In addition to these research efforts, a number of specific hardware needs were identified which will require development. These include heat pumps, low weight radiators, advanced heat pipes, stability enhancement devices, high heat flux evaporators, and liquid/vapor separators. Also identified was the need for a centralized source of reliable, up-to-date information on two-phase flow in a space environment.
Two-Phase Reactions in Microdroplets without the Use of Phase-Transfer Catalysts.
Yan, Xin; Cheng, Heyong; Zare, Richard N
2017-02-22
Many important chemical transformations occur in two-phase reactions, which are widely used in chemical, pharmaceutical, and polymer manufacturing. We present an efficient method for performing two-phase reactions in microdroplets sheared by sheath gas without using a phase-transfer catalyst. This avoids disadvantages such as thermal instability, high cost, and, especially, the need to separate and recycle the catalysts. We show that various alcohols can be oxidized to the corresponding aldehydes and ketones within milliseconds in moderate to good yields (50-75 %). The scale-up of the present method was achieved at an isolated rate of 1.2 mg min(-1) for the synthesis of 4-nitrobenzylaldehyde from 4-nitrobenzyl alcohol in the presence of sodium hypochlorite. The biphasic nature of this process, which avoids use of a phase-transfer catalyst, greatly enhances synthetic effectiveness.
Numerical Simulation of Two-Phase Critical Flow with the Phase Change in the Nozzle Tube
NASA Astrophysics Data System (ADS)
Ishigaki, Masahiro; Watanabe, Tadashi; Nakamura, Hideo
Two-phase critical flow in the nozzle tube is analyzed numerically by the best estimate code TRACE and the CFD code FLUENT, and the performance of the mass flow rate estimation by the numerical codes is discussed. For the best estimate analysis by the TRACE code, the critical flow option is turned on. The mixture model is used with the cavitation model and the evaporation-condensation model for the numerical simulation by the FLUENT code. Two test cases of the two-phase critical flow are analyzed. One case is the critical flashing flow in a convergent-divergent nozzle (Super Moby Dick experiment), and the other case is the break nozzle flow for a steam generator tube rupture experiment of pressurized water reactors at Large Scale Test Facility of Japan Atomic Energy Agency. The calculation results of the mass flow rates by the numerical simulations show good agreements with the experimental results.
Synchrotron 4-dimensional imaging of two-phase flow through porous media
Kim, F.H.; Penumadu, D.; Patel, P.; Xiao, X.; Garboczi, E.J.; Moylan, S.P.; Donmez, M.A.
2016-01-01
Near real-time visualization of complex two-phase flow in a porous medium was demonstrated with dynamic 4-dimensional (4D) (3D + time) imaging at the 2-BM beam line of the Advanced Photon Source (APS) at Argonne National Laboratory. Advancing fluid fronts through tortuous flow paths and their interactions with sand grains were clearly captured, and formations of air bubbles and capillary bridges were visualized. The intense X-ray photon flux of the synchrotron facility made 4D imaging possible, capturing the dynamic evolution of both solid and fluid phases. Computed Tomography (CT) scans were collected every 12 s with a pixel size of 3.25 µm. The experiment was carried out to improve understanding of the physics associated with two-phase flow. The results provide a source of validation data for numerical simulation codes such as Lattice-Boltzmann, which are used to model multi-phase flow through porous media. PMID:27891248
Measurement of average density and relative volumes in a dispersed two-phase fluid
Sreepada, S.R.; Rippel, R.R.
1990-12-19
An apparatus and a method are disclosed for measuring the average density and relative volumes in an essentially transparent, dispersed two-phase fluid. A laser beam with a diameter no greater than 1% of the diameter of the bubbles, droplets, or particles of the dispersed phase is directed onto a diffraction grating. A single-order component of the diffracted beam is directed through the two-phase fluid and its refraction is measured. Preferably, the refracted beam exiting the fluid is incident upon a optical filter with linearly varying optical density and the intensity of the filtered beam is measured. The invention can be combined with other laser-based measurement systems, e.g., laser doppler anemometry.
Targeted Delivery by Smart Capsules for Controlling Two-phase Flow in Porous Media
NASA Astrophysics Data System (ADS)
Fan, J.; Weitz, D.
2015-12-01
Understanding and controlling two-phase flow in porous media are of particular importance to the relevant industry applications, such as enhanced oil recovery, CO2 sequestration, and groundwater remediation. We develop a variety of smart microcapsules that can deliver and release specific substances to the target location in the porous medium, and therefore change the fluid property or medium geometry at certain locations. In this talk, I will present two types of smart capsules for (a) delivering surfactant to the vicinity of oil-water interface and (b) delivering microgels to the high permeability region and therefore blocking the pore space there, respectively. We also show that flooding these two capsules into porous media effectively reduces the trapped oil and improves the homogeneity of the medium, respectively. Besides of its industrial applications, this technique also opens a new window to study the mechanism of two-phase flow in porous media.
Dynamic characteristics of two-phase thermal control system for spacecraft
NASA Astrophysics Data System (ADS)
Malozemov, Vladimir V.; Kudryavtseva, Natal'ya S.; Antonov, Viktor A.; Zagar, Oleg V.; Chernobaev, Nikolaj N.
1992-07-01
This paper deals with review of the issues associated with modelling the dynamic processes in the spacecraft two-phase thermal control systems. The work presents the results of modelling the nonstationary conditions of the evaporative and condensation heat exchangers functioning, investigates their response to the characteristic external influences. Disclosed are the results of the computer-aided modelling the two-phase thermal control system with a pump. The dynamic characteristics of the change in the inputs of pressures, temperatures and vapor content of a coolant in various branches of the system, as well as the lengths of the heat transfer zones in the evaporator and condenser under effect of the typical disturbing actions are obtained. The attained transients are analyzed.
[The two-phase growth medium for sub-culturing of Helicobacter pylori].
Isaeva, G Sh; Aleshkin, V A; Sel'kova, E P; Gerasimova, M S; Moroz, P I
2013-06-01
A. Pylori is a very undemanding microorganism needing the in support of complex of conditions including particular atmosphere, temperature of culturing and composition of growth medium. The two-phase growth medium is recommended to sub-culturing in Petri dishes with diameter of 90 mm. The growth medium consists of chocolate agar with addition of Schedler broth and enriched with 10% serum of cattle.
Numerical Study of Two-Phase Flow Field in a Simplified Swirl Cup Combustor (Preprint)
2007-09-24
Article 3 . DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Numerical Study of Two-Phase Flow Field in a Simplified Swirl Cup...swirl provides a recirculation zone which enhances mixing and flame stability. Some high-performance aircraft engines such as in GE/SNECMA CFM56 ...downstream of a GE/SNECMA CFM56 engine combustor swirl cup in which the primary and secondary swirlers provide co-axial, counter-swirling airstreams
Multiphysics modeling of two-phase film boiling within porous corrosion deposits
Jin, Miaomiao Short, Michael
2016-07-01
Porous corrosion deposits on nuclear fuel cladding, known as CRUD, can cause multiple operational problems in light water reactors (LWRs). CRUD can cause accelerated corrosion of the fuel cladding, increase radiation fields and hence greater exposure risk to plant workers once activated, and induce a downward axial power shift causing an imbalance in core power distribution. In order to facilitate a better understanding of CRUD's effects, such as localized high cladding surface temperatures related to accelerated corrosion rates, we describe an improved, fully-coupled, multiphysics model to simulate heat transfer, chemical reactions and transport, and two-phase fluid flow within these deposits. Our new model features a reformed assumption of 2D, two-phase film boiling within the CRUD, correcting earlier models' assumptions of single-phase coolant flow with wick boiling under high heat fluxes. This model helps to better explain observed experimental values of the effective CRUD thermal conductivity. Finally, we propose a more complete set of boiling regimes, or a more detailed mechanism, to explain recent CRUD deposition experiments by suggesting the new concept of double dryout specifically in thick porous media with boiling chimneys. - Highlights: • A two-phase model of CRUD's effects on fuel cladding is developed and improved. • This model eliminates the formerly erroneous assumption of wick boiling. • Higher fuel cladding temperatures are predicted when accounting for two-phase flow. • Double-peaks in thermal conductivity vs. heat flux in experiments are explained. • A “double dryout” mechanism in CRUD is proposed based on the model and experiments.
Conceptual plan: Two-Phase Flow Laboratory Program for the Waste Isolation Pilot Plant
Howarth, S.M.
1993-07-01
The Salado Two-Phase Flow Laboratory Program was established to address concerns regarding two-phase flow properties and to provide WIPP-specific, geologically consistent experimental data to develop more appropriate correlations for Salado rock to replace those currently used in Performance Assessment models. Researchers in Sandia`s Fluid Flow and Transport Department originally identified and emphasized the need for laboratory measurements of Salado threshold pressure and relative permeability. The program expanded to include the measurement of capillary pressure, rock compressibility, porosity, and intrinsic permeability and the assessment of core damage. Sensitivity analyses identified the anhydrite interbed layers as the most likely path for the dissipation of waste-generated gas from waste-storage rooms because of their relatively high permeability. Due to this the program will initially focus on the anhydrite interbed material. The program may expand to include similar rock and flow measurements on other WIPP materials including impure halite, pure halite, and backfill and seal materials. This conceptual plan presents the scope, objectives, and historical documentation of the development of the Salado Two-Phase Flow Program through January 1993. Potential laboratory techniques for assessing core damage and measuring porosity, rock compressibility, capillary and threshold pressure, permeability as a function of stress, and relative permeability are discussed. Details of actual test designs, test procedures, and data analysis are not included in this report, but will be included in the Salado Two-Phase Flow Laboratory Program Test Plan pending the results of experimental and other scoping activities in FY93.
An Evaluation of Liquid and Two-Phase Cooling Techniques for Use in Electrical Machinery.
1984-12-01
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Coupling of two-phase flow in fractured-vuggy reservoir with filling medium
NASA Astrophysics Data System (ADS)
Xie, Haojun; Li, Aifen; Huang, Zhaoqin; Gao, Bo; Peng, Ruigang
2017-01-01
Caves in fractured-vuggy reservoir usually contain lots of filling medium, so the two-phase flow in formations is the coupling of free flow and porous flow, and that usually leads to low oil recovery. Considering geological interpretation results, the physical filled cave models with different filling mediums are designed. Through physical experiment, the displacement mechanism between un-filled areas and the filling medium was studied. Based on the experiment model, we built a mathematical model of laminar two-phase coupling flow considering wettability of the porous media. The free fluid region was modeled using the Navier-Stokes and Cahn-Hilliard equations, and the two-phase flow in porous media used Darcy's theory. Extended BJS conditions were also applied at the coupling interface. The numerical simulation matched the experiment very well, so this numerical model can be used for two-phase flow in fracture-vuggy reservoir. In the simulations, fluid flow between inlet and outlet is free flow, so the pressure difference was relatively low compared with capillary pressure. In the process of water injection, the capillary resistance on the surface of oil-wet filling medium may hinder the oil-water gravity differentiation, leading to no fluid exchange on coupling interface and remaining oil in the filling medium. But for the water-wet filling medium, capillary force on the surface will coordinate with gravity. So it will lead to water imbibition and fluid exchange on the interface, high oil recovery will finally be reached at last.
Analysis of pulsating spray flames propagating in lean two-phase mixtures with unity Lewis number
Nicoli, C.; Haldenwang, P.; Suard, S.
2005-11-01
Pulsating (or oscillatory) spray flames have recently been observed in experiments on two-phase combustion. Numerical studies have pointed out that such front oscillations can be obtained even with very simple models of homogeneous two-phase mixtures, including elementary vaporization schemes. The paper presents an analytical approach within the simple framework of the thermal-diffusive model, which is complemented by a vaporization rate independent of gas temperature, as soon as the latter reaches a certain thermal threshold ({theta}{sub v} in reduced form). The study involves the Damkoehler number (Da), the ratio of chemical reaction rate to vaporization rate, and the Zeldovich number (Ze) as essential parameters. We use the standard asymptotic method based on matched expansions in terms of 1/Ze. Linear analysis of two-phase flame stability is performed by studying, in the absence of differential diffusive effects (unity Lewis number), the linear growth rate of 2-D perturbations added to steady plane solutions and characterized by wavenumber k in the direction transverse to spreading. A domain of existence is found for the pulsating regime. It corresponds to mixture characteristics often met in air-fuel two-phase systems: low boiling temperature ({theta}{sub v} << 1), reaction rate not higher than vaporization rate (Da < 1, i.e., small droplets), and activation temperature assumed to be high compared with flame temperature (Ze {>=} 10). Satisfactory comparison with numerical simulations confirms the validity of the analytical approach; in particular, positive growth rates have been found for planar perturbations (k = 0) and for wrinkled fronts (k {ne} 0). Finally, comparison between predicted frequencies and experimental measurements is discussed.
Lattice Boltzmann Methods to Address Fundamental Boiling and Two-Phase Problems
Uddin, Rizwan
2012-01-01
This report presents the progress made during the fourth (no cost extension) year of this three-year grant aimed at the development of a consistent Lattice Boltzmann formulation for boiling and two-phase flows. During the first year, a consistent LBM formulation for the simulation of a two-phase water-steam system was developed. Results of initial model validation in a range of thermo-dynamic conditions typical for Boiling Water Reactors (BWRs) were shown. Progress was made on several fronts during the second year. Most important of these included the simulation of the coalescence of two bubbles including the surface tension effects. Work during the third year focused on the development of a new lattice Boltzmann model, called the artificial interface lattice Boltzmann model (AILB model) for the 3 simulation of two-phase dynamics. The model is based on the principle of free energy minimization and invokes the Gibbs-Duhem equation in the formulation of non-ideal forcing function. This was reported in detail in the last progress report. Part of the efforts during the last (no-cost extension) year were focused on developing a parallel capability for the 2D as well as for the 3D codes developed in this project. This will be reported in the final report. Here we report the work carried out on testing the AILB model for conditions including the thermal effects. A simplified thermal LB model, based on the thermal energy distribution approach, was developed. The simplifications are made after neglecting the viscous heat dissipation and the work done by pressure in the original thermal energy distribution model. Details of the model are presented here, followed by a discussion of the boundary conditions, and then results for some two-phase thermal problems.
A Family of Reference Hugoniots for Two-phase Porous Materials
2015-06-01
UNCLASSIFIED UNCLASSIFIED A Family of Reference Hugoniots for Two-phase Porous Materials A.D. Resnyansky Weapons and Combat...of Australia 2015 AR-016-394 June 2015 APPROVED FOR PUBLIC RELEASE UNCLASSIFIED UNCLASSIFIED A Family of Reference Hugoniots for...EOS [4] is based on a constitutive consideration. The latter approach specifies Hugoniot states from a family of non-equilibrium Hugoniot for a
Analysis of the Hydrodynamics and Heat Transfer Aspects of Microgravity Two-Phase Flows
NASA Technical Reports Server (NTRS)
Rezkallah, Kamiel S.
1996-01-01
Experimental results for void fractions, flow regimes, and heat transfer rates in two-phase, liquid-gas flows are summarized in this paper. The data was collected on-board NASA's KC-135 reduced gravity aircraft in a 9.525 mm circular tube (i.d.), uniformly heated at the outer surface. Water and air flows were examined as well as three glycerol/water solutions and air. Results are reported for the water-air data.
A Heat Transfer Investigation of Liquid and Two-Phase Methane
NASA Technical Reports Server (NTRS)
VanNoord, Jonathan
2010-01-01
A heat transfer investigation was conducted for liquid and two-phase methane. The tests were conducted at the NASA Glenn Research Center Heated Tube Facility (HTF) using resistively heated tube sections to simulate conditions encountered in regeneratively cooled rocket engines. This testing is part of NASA s Propulsion and Cryogenics Advanced Development (PCAD) project. Nontoxic propellants, such as liquid oxygen/liquid methane (LO2/LCH4), offer potential benefits in both performance and safety over equivalently sized hypergolic propulsion systems in spacecraft applications. Regeneratively cooled thrust chambers are one solution for high performance, robust LO2/LCH4 engines, but cooling data on methane is limited. Several test runs were conducted using three different diameter Inconel 600 tubes, with nominal inner diameters of 0.0225-, 0.054-, and 0.075-in. The mass flow rate was varied from 0.005 to 0.07 lbm/sec. As the current focus of the PCAD project is on pressure fed engines for LO2/LCH4, the average test section outlet pressures were targeted to be 200 psia or 500 psia. The heat flux was incrementally increased for each test condition while the test section wall temperatures were monitored. A maximum average heat flux of 6.2 Btu/in.2 sec was achieved and, at times, the temperatures of the test sections reached in excess of 1800 R. The primary objective of the tests was to produce heat transfer correlations for methane in the liquid and two-phase regime. For two-phase flow testing, the critical heat flux values were determined where the fluid transitions from nucleate boiling to film boiling. A secondary goal of the testing was to measure system pressure drops in the two-phase regime.
Interfacial Tension Effect on Cell Partition in Aqueous Two-Phase Systems.
Atefi, Ehsan; Joshi, Ramila; Mann, Jay Adin; Tavana, Hossein
2015-09-30
Aqueous two-phase systems (ATPS) provide a mild environment for the partition and separation of cells. We report a combined experimental and theoretical study on the effect of interfacial tension of polymeric ATPS on the partitioning of cells between two phases and their interface. Two-phase systems are generated using polyethylene glycol and dextran of specific properties as phase-forming polymers and culture media as the solvent component. Ultralow interfacial tensions of the solutions are precisely measured using an axisymmetric drop shape analysis method. Partition experiments show that two-phase systems with an interfacial tension of 30 μJ/m(2) result in distribution of majority of cells to the bottom dextran phase. An increase in the interfacial tension results in a distribution of cells toward the interface. An independent cancer cell spheroid formation assay confirms these observations: a drop of the dextran phase containing cancer cells is dispensed into the immersion polyethylene glycol phase to form a cell-containing drop. Only at very small interfacial tensions do cells remain within the drop to aggregate into a spheroid. We perform a thermodynamic modeling of cell partition to determine variations of free energy associated with displacement of cells in ATPS with respect to the ultralow interfacial tensions. This modeling corroborates with the experimental results and demonstrates that at the smallest interfacial tension of 30 μJ/m(2), the free energy is a minimum with cells in the bottom phase. Increasing the interfacial tension shifts the minimum energy and partition of cells toward the interfacial region of the two aqueous phases. Examining differences in the partition behavior and minimum free energy modeling of A431.H9 cancer cells and mouse embryonic stem cells shows that the surface properties of cells further modulate partition in ATPS. This combined approach provides a fundamental understanding of interfacial tension role on cell partition in
The growth of vapor bubble and relaxation between two-phase bubble flow
NASA Astrophysics Data System (ADS)
Mohammadein, S. A.; Subba Reddy Gorla, Rama
2002-10-01
This paper presents the behavior of the bubble growth and relaxation between vapor and superheated liquid. The growth and thermal relaxation time between the two-phases are obtained for different levels of superheating. The heat transfer problem is solved numerically by using the extended Scriven model. Results are compared with those of Scriven theory and MOBY DICK experiment with reasonably good agreement for lower values of superheating.
Analytical study on two-phase MHD flow of electrically conducting magnetic fluid
Okubo, Masaaki; Ishimoto, Jun; Nishiyama, Hideya; Kamiyama, Shinichi
1994-01-01
An energy conversion system using magnetic fluids proposed by Resler and Rosensweig was based on the principle that the magnetization of magnetic fluids changes with temperature. However, significant results have not been obtained up to the present. To overcome this limit and to increase the acceleration of fluid flow the authors have contributed a new energy conversion system using two-phase flow produced by heat addition. This idea came from the two-phase liquid-metal MHD power generation system proposed by Petrick and Branover. If temperature sensitive magnetic fluids are used, such a system can produce a larger force than conventional systems because the properties of apparent magnetization change not only by temperature rise but also by gas inclusion. In the present paper, an analytical study is extended to the case of electrically conducting magnetic fluid as a basic study for demonstrating the possibility of application of electrically conducting magnetic fluid to working fluid in a liquid-metal MHD power generation system. Electrically conducting magnetic fluid is usually prepared by dispersing fine iron particles into a liquid metal such as mercury. To prevent a solidification of particles and keep a homogeneous dispersion, a thin film of tin is attached to the particle`s surface. Thus the electrically conducting liquid behaves as fluid itself having magnetization. The equations governing a one-dimensional boiling two-phase duct flow of such an electrically conducting magnetic fluid in a traverse magnetic field are numerically solved. The analytical results of the two-phase flow characteristics of the magnetic fluid are compared with ones of an electrically conducting nonmagnetic fluid.
Two-phase flow and heat transfer in porous beds under variable body forces, part 7
NASA Technical Reports Server (NTRS)
Henry, H. R.
1970-01-01
The design of an experiment to determine the behavior of two-phase vapor-liquid and gas-liquid flow through porous beds in low gravity environments is discussed. The selection of porous materials, liquids, and gases is described. The parameters necessary for the design and development of a flight experimental system are examined. The general specifications for system elements requiring additional development are identified.
Two-Phase Working Fluids for the Temperature Range 50 to 350 C
NASA Technical Reports Server (NTRS)
Saaski, E. W.; Owzarski, P. C.
1977-01-01
The decomposition and corrosion of two-phase heat transfer liquids and metal envelopes have been investigated on the basis of molecular bond strengths and chemical thermodynamics. Potentially stable heat transfer fluids for the temperature range 100 C to 350 C have been identified, and reflux heat pipes tests initiated with 10 fluids and carbon steel and aluminum envelopes to experimentally establish corrosion behavior and noncondensable gas generation rates.
Modelling of two-phase flow in a minichannel using level-set method
NASA Astrophysics Data System (ADS)
Grzybowski, H.; Mosdorf, R.
2014-08-01
Today there is a great interest in micro-scale multiphase fluid flow. In the paper, the numerical simulation of two-phase flow inside 3 mm minichannel was carried out. The liquid- gas interface was captured using the level-set method. During the calculation, the stabilization and reinitialization of level set function was performed in order to obtain the proper accuracy of the simulation. Incompressible Navier-Stokes equations were solved using the COMSOL Multiphysics® on a two-dimensional mesh. The process of formation of different two-phase flow patterns in the minichannel has been investigated. During the simulation it has been analysed three flow patterns: the bubbly flow and two kinds of slug flow with short and long slugs. It has been shown that unsteady flow at the inlet of the minichannel is responsible for the chaotic character of changes of the slug and bubble sizes. Such unsteady flow modifies the distance between the bubbles and slugs. It has been shown that for the low water inlet velocity the two-phase flow pattern becomes more stable.
Central Upwind Scheme for a Compressible Two-Phase Flow Model
Ahmed, Munshoor; Saleem, M. Rehan; Zia, Saqib; Qamar, Shamsul
2015-01-01
In this article, a compressible two-phase reduced five-equation flow model is numerically investigated. The model is non-conservative and the governing equations consist of two equations describing the conservation of mass, one for overall momentum and one for total energy. The fifth equation is the energy equation for one of the two phases and it includes source term on the right-hand side which represents the energy exchange between two fluids in the form of mechanical and thermodynamical work. For the numerical approximation of the model a high resolution central upwind scheme is implemented. This is a non-oscillatory upwind biased finite volume scheme which does not require a Riemann solver at each time step. Few numerical case studies of two-phase flows are presented. For validation and comparison, the same model is also solved by using kinetic flux-vector splitting (KFVS) and staggered central schemes. It was found that central upwind scheme produces comparable results to the KFVS scheme. PMID:26039242
Two-phase Flow Ejector as Water Refrigerant by Using Waste Heat
NASA Astrophysics Data System (ADS)
Yamanaka, H.; Nakagawa, M.
2013-04-01
Energy saving and the use of clean energy sources have recently become significant issues. It is expected that clean energy sources such as solar panels and fuel cells will be installed in many private dwellings. However, when electrical power is generated, exhaust heat is simultaneously produced. Especially for the summer season, the development of refrigeration systems that can use this waste heat is highly desirable. One approach is an ejector that can reduce the mechanical compression work required in a normal refrigeration cycle. We focus on the use of water as a refrigerant, since this can be safely implemented in private dwellings. Although the energy conversion efficiency is low, it is promising because it can use heat that would otherwise be discarded. However, a steam ejector refrigeration cycle requires a large amount of energy to change saturated water into vapour. Thus, we propose a more efficient two-phase flow ejector cycle. Experiments were carried out in which the quality of the two-phase flow from a tank was varied, and the efficiency of the ejector and nozzle was determined. The results show that a vacuum state can be achieved and suction exerted with a two-phase flow state at the ejector nozzle inlet.
de Brito Cardoso, Gustavo; Souza, Isabela Nascimento; Pereira, Matheus M; Freire, Mara G; Soares, Cleide Mara Faria; Lima, Álvaro Silva
2014-11-05
In this work, it is shown that novel aqueous two-phase systems can be formed by the combination of acetonitrile and polysaccharides, namely dextran. Several ternary phase diagrams were determined at 25 °C for the systems composed of water + acetonitrile + dextran. The effect of the dextran molecular weight (6,000, 40,000 and 100,000 g.mol(-1)) was ascertained toward their ability to undergo liquid-liquid demixing. An increase in the dextran molecular weight favors the phase separation. Furthermore, the effect of temperature (25, 35 and 45 °C) was evaluated for the system constituted by the dextran of higher molecular weight. Lower temperatures are favorable for phase separation since lower amounts of dextran and acetonitrile are required for the creation of aqueous two-phase systems. In general, acetonitrile is enriched in the top phase while dextran is majorly concentrated in the bottom phase. The applicability of this new type of two-phase systems as liquid-liquid extraction approaches was also evaluated by the study of the partition behavior of a well-known antioxidant - vanillin - and used here as a model biomolecule. The optimized conditions led to an extraction efficiency of vanillin of 95% at the acetonitrile-rich phase.
Two-phase flow patterns characteristics analysis based on image and conductance sensors
NASA Astrophysics Data System (ADS)
Wang, Zhenya; Jin, Ningde; Wang, Chun; Wang, Jinxiang
2008-10-01
In order to study the temporal and spatial evolution characteristics of gas-liquid two-phase flow pattern, the two-phase flow monitoring system composed of high-speed dynamic camera and Vertical Multi-Electrode Array conductance sensor (VMEA) was utilized to shoot dynamic images and acquire the conductance fluctuating signals of 5 typical vertical gas-liquid two-phase flow patterns in a 125mm i.d. upward pipe. Gray level co-occurrence matrix (GLCM) was used to extract four time-varying characteristic parameter indices which represented different flow image texture structures and also Lempel-Ziv complexity of them were calculated. Then the transition of flow structure and flow property were comprehensively analyzed, combining the result derived from image information with recurrence plots (RPs) and Lempel-Ziv complexity of conductance fluctuating signals. The study showed that the line texture structure of RPs enabled to indicate flow pattern characteristics; the flow image texture structure characteristic parameters sequence described the variance of flow structure and dynamical complexity of different flow patterns.
Optical readout of a two phase liquid argon TPC using CCD camera and THGEMs
NASA Astrophysics Data System (ADS)
Mavrokoridis, K.; Ball, F.; Carroll, J.; Lazos, M.; McCormick, K. J.; Smith, N. A.; Touramanis, C.; Walker, J.
2014-02-01
This paper presents a preliminary study into the use of CCDs to image secondary scintillation light generated by THick Gas Electron Multipliers (THGEMs) in a two phase LAr TPC. A Sony ICX285AL CCD chip was mounted above a double THGEM in the gas phase of a 40 litre two-phase LAr TPC with the majority of the camera electronics positioned externally via a feedthrough. An Am-241 source was mounted on a rotatable motion feedthrough allowing the positioning of the alpha source either inside or outside of the field cage. Developed for and incorporated into the TPC design was a novel high voltage feedthrough featuring LAr insulation. Furthermore, a range of webcams were tested for operation in cryogenics as an internal detector monitoring tool. Of the range of webcams tested the Microsoft HD-3000 (model no:1456) webcam was found to be superior in terms of noise and lowest operating temperature. In ambient temperature and atmospheric pressure 1 ppm pure argon gas, the THGEM gain was ≈ 1000 and using a 1 msec exposure the CCD captured single alpha tracks. Successful operation of the CCD camera in two-phase cryogenic mode was also achieved. Using a 10 sec exposure a photograph of secondary scintillation light induced by the Am-241 source in LAr has been captured for the first time.
A 3D moving mesh Finite Element Method for two-phase flows
NASA Astrophysics Data System (ADS)
Anjos, G. R.; Borhani, N.; Mangiavacchi, N.; Thome, J. R.
2014-08-01
A 3D ALE Finite Element Method is developed to study two-phase flow phenomena using a new discretization method to compute the surface tension forces. The computational method is based on the Arbitrary Lagrangian-Eulerian formulation (ALE) and the Finite Element Method (FEM), creating a two-phase method with an improved model for the liquid-gas interface. An adaptive mesh update procedure is also proposed for effective management of the mesh to remove, add and repair elements, since the computational mesh nodes move according to the flow. The ALE description explicitly defines the two-phase interface position by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The proposed methodology for computing the curvature leads to accurate results with moderate programming effort and computational cost. Static and dynamic tests have been carried out to validate the method and the results have compared well to analytical solutions and experimental results found in the literature, demonstrating that the new proposed methodology provides good accuracy to describe the interfacial forces and bubble dynamics. This paper focuses on the description of the proposed methodology, with particular emphasis on the discretization of the surface tension force, the new remeshing technique, and the validation results. Additionally, a microchannel simulation in complex geometry is presented for two elongated bubbles.
Binary image encryption based on interference of two phase-only masks.
Jia, Wei; Wen, Fung Jacky; Chow, Yuk Tak; Zhou, Changhe
2012-07-20
Optical image encryption based on interference has attracted a lot of attention recently. The technique employs two pure phase masks derived from the complex field of the image in the Fresnel diffraction domain. The image decryption procedure can be carried out by inverse Fresnel transformation of the summation of two pure phase masks. However, the silhouette of the original image, which is recovered by either of the two phase-only masks, impedes the application of this technique. In this paper, a very simple method for binary image encryption based on interference of two phase-only masks is proposed without any silhouette problem. The binary image in combination with a random phase mask is separated into two phase-only masks directly, and the decryption by summation of the two masks can be performed digitally or optically. In this paper, the encryption and decryption processes are analyzed, after which both the optical simulation and the experimental results based on single-beam holography are given to demonstrate the feasibility of the encryption method. As information nowadays is mainly digitized into binary codes, the proposed encryption method may find applications in the information processing field.
A Simple and Efficient Diffuse Interface Method for Compressible Two-Phase Flows
Ray A. Berry; Richard Saurel; Fabien Petitpas
2009-05-01
In nuclear reactor safety and optimization there are key issues that rely on in-depth understanding of basic two-phase flow phenomena with heat and mass transfer. For many reasons, to be discussed, there is growing interest in the application of two-phase flow models to provide diffuse, but nevertheless resolved, simulation of interfaces between two immiscible compressible fluids – diffuse interface method (DIM). Because of its ability to dynamically create interfaces and to solve interfaces separating pure media and mixtures for DNS-like (Direct Numerical Simulation) simulations of interfacial flows, we examine the construction of a simple, robust, fast, and accurate numerical formulation for the 5-equation Kapila et al. [1] reduced two-phase model. Though apparently simple, the Kapila et al. model contains a volume fraction differential transport equation containing a nonlinear, non-conservative term which poses serious computational challenges. To circumvent the difficulties encountered with the single velocity and single pressure Kapila et al. [1] multiphase flow model, a 6-equation relaxation hyperbolic model is built to solve interface problems with compressible fluids. In this approach, pressure non-equilibrium is first restored, followed by a relaxation to an asymptotic solution which is convergent to the solutions of the Kapila et al. reduced model. The apparent complexity introduced with this extended hyperbolic model actually leads to considerable simplifications regarding numerical resolution, and the various ingredients used by this method are general enough to consider future extensions to problems involving complex physics.
Comparison of Pressure Drop between Calculation and Experiment for a Two-phase Carbon Dioxide Loop
NASA Astrophysics Data System (ADS)
Mo, D.-C.; Xiao, W.-J.; Huang, Z.-C.; Sun, X.-H.; Chen, Y.; Lu, S.-S.; Li, T.-X.; Qi, X.-M.; Wang, Z.-X.; Pauw, A.; Bsibsi, M.; Gargiulo, C.; van Es, J.; He, Z.-H.
2008-09-01
Tracker thermal control system (TTCS) is an active-pumped two-phase carbon dioxide cooling loop, which is developed for the Alpha Magnetic Spectrometer tracker front-end electronics. The maintenance-free centrifugal pump is a critical component in the design mainly due to the limited pressure head with small mass flows. Therefore a correct pressure drop is required to predict the pressure drop for dynamic modeling. As the normal operational temperature of the carbon dioxide in the TTCS is from - 15°C to +15°C, which is very close to its critical point, 33°C, and many two-phase pressure drop correlations may not fit well here. In this paper, we attempt to correlate the pressure drops between the calculations and the experiment of the two-phase CO2 loop. The comparison will focus on one evaporator. Here, the Lockhart/Martinelli correlation is recorrelated with different definition C value for CO2 according to the test results. Comparison shows that, the new correlation can fit the test results well.
The effect of spontaneous curvature on a two-phase vesicle
Cox, Geoffrey; Lowengrub, John
2015-01-01
Vesicles are membrane-bound structures commonly known for their roles in cellular transport and the shape of a vesicle is determined by its surrounding membrane (lipid bilayer). When the membrane is composed of different lipids, it is natural for the lipids of similar molecular structure to migrate towards one another (via spinodal decomposition), creating a multi-phase vesicle. In this article, we consider a two-phase vesicle model which is driven by nature’s propensity to maintain a minimal state of elastic energy. The model assumes a continuum limit, thereby treating the membrane as a closed three-dimensional surface. The main purpose of this study is to reveal the complexity of the Helfrich two-phase vesicle model with non-zero spontaneous curvature and provide further evidence to support the relevance of spontaneous curvature as a modelling parameter. In this paper, we illustrate the complexity of the Helfrich two-phase model by providing multiple examples of undocumented solutions and energy hysteresis. We also investigate the influence of spontaneous curvature on morphological effects and membrane phenomena such as budding and fusion. PMID:26097287
Aqueous Two-Phase Systems formed by Biocompatible and Biodegradable Polysaccharides and Acetonitrile
de Brito Cardoso, Gustavo; Souza, Isabela Nascimento; Pereira, Matheus M.; Freire, Mara G.; Soares, Cleide Mara Faria; Lima, Álvaro Silva
2015-01-01
In this work, it is shown that novel aqueous two-phase systems can be formed by the combination of acetonitrile and polysaccharides, namely dextran. Several ternary phase diagrams were determined at 25 °C for the systems composed of water + acetonitrile + dextran. The effect of the dextran molecular weight (6,000, 40,000 and 100,000 g.mol−1) was ascertained toward their ability to undergo liquid-liquid demixing. An increase in the dextran molecular weight favors the phase separation. Furthermore, the effect of temperature (25, 35 and 45 °C) was evaluated for the system constituted by the dextran of higher molecular weight. Lower temperatures are favorable for phase separation since lower amounts of dextran and acetonitrile are required for the creation of aqueous two-phase systems. In general, acetonitrile is enriched in the top phase while dextran is majorly concentrated in the bottom phase. The applicability of this new type of two-phase systems as liquid-liquid extraction approaches was also evaluated by the study of the partition behavior of a well-known antioxidant – vanillin - and used here as a model biomolecule. The optimized conditions led to an extraction efficiency of vanillin of 95% at the acetonitrile-rich phase. PMID:25729320
Internal structure and interfacial area in two-phase flow systems
Kojasoy, G.
1991-01-01
The interfacial transfer terms and the importance of the interfacial area concentration are reviewed first with respect to the two-fluid model formulation of two-phase flow systems. Then the available measurement techniques for interfacial area are reviewed. At present, it appears that various methods such as the chemical, light attenuation, photographic, ultrasound attenuation and probe techniques have a number of limitations. Among these measurement techniques, however, the local probe method using one or more double sensors seems to have the greatest potential in terns of accuracy and wider applicability in various two-phase flow patterns. From the brief review of existing interfacial area modeling methods, it is concluded that the conventional approaches might not be sufficient, and new directions are indicated. Recent experimental results on local interfacial structural characteristics of horizontal bubbly two-phase flow and internal flow structure development are presented. More specifically, experimental results on local void fraction, interfacial area concentration, bubble size, bubble interface velocity and bubble frequency are documented in detail. Finally, a theoretical model predicting the mean bubble size and interfacial area concentration is proposed. The theoretically predicted bubble size and interfacial area concentration are found to agree reasonably well with those measured by using a double-sensor resistivity technique.
Internal structure and interfacial area in two-phase flow systems
Kojasoy, G.
1991-12-31
The interfacial transfer terms and the importance of the interfacial area concentration are reviewed first with respect to the two-fluid model formulation of two-phase flow systems. Then the available measurement techniques for interfacial area are reviewed. At present, it appears that various methods such as the chemical, light attenuation, photographic, ultrasound attenuation and probe techniques have a number of limitations. Among these measurement techniques, however, the local probe method using one or more double sensors seems to have the greatest potential in terns of accuracy and wider applicability in various two-phase flow patterns. From the brief review of existing interfacial area modeling methods, it is concluded that the conventional approaches might not be sufficient, and new directions are indicated. Recent experimental results on local interfacial structural characteristics of horizontal bubbly two-phase flow and internal flow structure development are presented. More specifically, experimental results on local void fraction, interfacial area concentration, bubble size, bubble interface velocity and bubble frequency are documented in detail. Finally, a theoretical model predicting the mean bubble size and interfacial area concentration is proposed. The theoretically predicted bubble size and interfacial area concentration are found to agree reasonably well with those measured by using a double-sensor resistivity technique.
Two-phase gas-liquid flow characteristics inside a plate heat exchanger
Nilpueng, Kitti; Wongwises, Somchai
2010-11-15
In the present study, the air-water two-phase flow characteristics including flow pattern and pressure drop inside a plate heat exchanger are experimentally investigated. A plate heat exchanger with single pass under the condition of counter flow is operated for the experiment. Three stainless steel commercial plates with a corrugated sinusoidal shape of unsymmetrical chevron angles of 55 and 10 are utilized for the pressure drop measurement. A transparent plate having the same configuration as the stainless steel plates is cast and used as a cover plate in order to observe the flow pattern inside the plate heat exchanger. The air-water mixture flow which is used as a cold stream is tested in vertical downward and upward flow. The results from the present experiment show that the annular-liquid bridge flow pattern appeared in both upward and downward flows. However, the bubbly flow pattern and the slug flow pattern are only found in upward flow and downward flow, respectively. The variation of the water and air velocity has a significant effect on the two-phase pressure drop. Based on the present data, a two-phase multiplier correlation is proposed for practical application. (author)
Two-phase flow in geothermal energy sources. Final technical report
Not Available
1981-07-01
A geothermal well consisting of single and two-phase flow sections was modeled in order to explore the variables important to the process. For this purpose a computer program was developed in a versatile form in order to be able to incorporate a variety of two phase flow void fraction and friction correlations. A parametric study indicated that the most significant variables controlling the production rate are: hydrostatic pressure drop or void fraction in the two-phase mixture; and, heat transfer from the wellbore to the surrounding earth. Downhole instrumentation was developed and applied in two flowing wells to provide experimental data for the computer program. The wells (East Mesa 8-1, and a private well) behaved differently. Well 8-1 did not flash and numerous shakedown problems in the probe were encountered. The private well did flash and the instrumentation detected the onset of flashing. A Users Manual was developed and presented in a workshop held in conjunction with the Geothermal Resources Council.
A Novel Hyperbolization Procedure for The Two-Phase Six-Equation Flow Model
Samet Y. Kadioglu; Robert Nourgaliev; Nam Dinh
2011-10-01
We introduce a novel approach for the hyperbolization of the well-known two-phase six equation flow model. The six-equation model has been frequently used in many two-phase flow applications such as bubbly fluid flows in nuclear reactors. One major drawback of this model is that it can be arbitrarily non-hyperbolic resulting in difficulties such as numerical instability issues. Non-hyperbolic behavior can be associated with complex eigenvalues that correspond to characteristic matrix of the system. Complex eigenvalues are often due to certain flow parameter choices such as the definition of inter-facial pressure terms. In our method, we prevent the characteristic matrix receiving complex eigenvalues by fine tuning the inter-facial pressure terms with an iterative procedure. In this way, the characteristic matrix possesses all real eigenvalues meaning that the characteristic wave speeds are all real therefore the overall two-phase flowmodel becomes hyperbolic. The main advantage of this is that one can apply less diffusive highly accurate high resolution numerical schemes that often rely on explicit calculations of real eigenvalues. We note that existing non-hyperbolic models are discretized mainly based on low order highly dissipative numerical techniques in order to avoid stability issues.
Investigation of Two-Phase Flows in Piping Bends and Elbows
NASA Technical Reports Server (NTRS)
Duncan, Allen B.; Sciascia, Vincent M.
1996-01-01
An experimental investigation of the hydrodynamic characteristics of two-phase R-113 flow has been carried out. Straight tube pressure drop data, as a function of mass flow rate (mass flux) and flow quality has been obtained using the Two-Phase Flow Test Facility located in the Advanced Thermal Laboratories of the Crew and Thermal Systems Division at the Lyndon B. Johnson Space Center. Additionally, after successfully obtaining the straight tube pressure drop data, the test facility was modified in order to obtain pressure drop data for the flow of two-phase R-113 through 180 deg piping bends. Inherent instabilities of the test facility prevented the successful acquisition of pressure drop data through the piping bends. The experimental straight tube data will be presented and compared with existing predictive correlations in an attempt to gain insight into the utility of such correlations as the basis for developing design criteria. A discussion of the instabilities which rendered successful acquisition of the piping bend data will be presented and suggestions will be made for eliminating these system tendencies. Finally, recommendations for future investigations, based on successful reconfiguration of the test facility, will be made.
Analysis of nanoscale two-phase flow of argon using molecular dynamics
Verma, Abhishek Kumar; Kumar, Rakesh
2014-12-09
Two phase flows through micro and nanochannels have attracted a lot of attention because of their immense applicability to many advanced fields such as MEMS/NEMS, electronic cooling, bioengineering etc. In this work, a molecular dynamics simulation method is employed to study the condensation process of superheated argon vapor force driven flow through a nanochannel combining fluid flow and heat transfer. A simple and effective particle insertion method is proposed to model phase change of argon based on non-periodic boundary conditions in the simulation domain. Starting from a crystalline solid wall of channel, the condensation process evolves from a transient unsteady state where we study the influence of different wall temperatures and fluid wall interactions on interfacial and heat transport properties of two phase flows. Subsequently, we analyzed transient temperature, density and velocity fields across the channel and their dependency on varying wall temperature and fluid wall interaction, after a dynamic equilibrium is achieved in phase transition. Quasi-steady nonequilibrium temperature profile, heat flux and interfacial thermal resistance were analyzed. The results demonstrate that the molecular dynamics method, with the proposed particle insertion method, effectively solves unsteady nonequilibrium two phase flows at nanoscale resolutions whose interphase between liquid and vapor phase is typically of the order of a few molecular diameters.
Effects of bubble–liquid two-phase turbulent hydrodynamics on cell damage in sparged bioreactor.
Liu, Yang; Li, Fanxing; Hu, Weiwei; Wiltberger, Kelly; Ryll, Thomas
2014-01-01
According to recent experimental studies on sparged bioreactors, significant cell damage may occur at the gas inlet region near the sparger. Although shear stress was proposed to be one of the potential causes for cell damage, detailed hydrodynamic studies at the gas inlet region of gas–liquid bioreactors have not been performed to date. In this work, a second-order moment (SOM) bubble–liquid two-phase turbulent model based on the two-fluid continuum approach is used to investigate the gas–liquid hydrodynamics in the bubble column reactor and their potential impacts on cell viability, especially at the gas inlet region. By establishing fluctuation velocity and bubble–liquid two-phase fluctuation velocities correlation transport equations, the anisotropy of two-phase stresses and the bubble– liquid interactions are fully considered. Simulation results from the SOM model indicate that shear and normal stresses, turbulent energy dissipation rate, and the turbulent kinetic energy are generally smaller at the gas inlet region when compared with those in the fully developed region. In comparison, a newly proposed correlation expression, stress-induced turbulent energy production (STEP), is found to correlate well with the unusually high cell death rate at the gas inlet region. Therefore, STEP, which represents turbulent energy transfer to a controlled volume induced by a combination of shear and normal stresses, has the potential to provide better explanation for increased cell death at the sparger region.
Analysis of nanoscale two-phase flow of argon using molecular dynamics
NASA Astrophysics Data System (ADS)
Verma, Abhishek Kumar; Kumar, Rakesh
2014-12-01
Two phase flows through micro and nanochannels have attracted a lot of attention because of their immense applicability to many advanced fields such as MEMS/NEMS, electronic cooling, bioengineering etc. In this work, a molecular dynamics simulation method is employed to study the condensation process of superheated argon vapor force driven flow through a nanochannel combining fluid flow and heat transfer. A simple and effective particle insertion method is proposed to model phase change of argon based on non-periodic boundary conditions in the simulation domain. Starting from a crystalline solid wall of channel, the condensation process evolves from a transient unsteady state where we study the influence of different wall temperatures and fluid wall interactions on interfacial and heat transport properties of two phase flows. Subsequently, we analyzed transient temperature, density and velocity fields across the channel and their dependency on varying wall temperature and fluid wall interaction, after a dynamic equilibrium is achieved in phase transition. Quasi-steady nonequilibrium temperature profile, heat flux and interfacial thermal resistance were analyzed. The results demonstrate that the molecular dynamics method, with the proposed particle insertion method, effectively solves unsteady nonequilibrium two phase flows at nanoscale resolutions whose interphase between liquid and vapor phase is typically of the order of a few molecular diameters.
Preparative crystallization of a single chain antibody using an aqueous two-phase system.
Huettmann, Hauke; Berkemeyer, Matthias; Buchinger, Wolfgang; Jungbauer, Alois
2014-11-01
A simultaneous crystallization and aqueous two-phase extraction of a single chain antibody was developed, demonstrating process integration. The process conditions were designed to form an aqueous two-phase system, and to favor crystallization, using sodium sulfate and PEG-2000. At sufficiently high concentrations of PEG, a second phase was generated in which the protein crystallization occurred simultaneously. The single chain antibody crystals were partitioned to the top, polyethylene glycol-rich phase. The crystal nucleation took place in the sodium sulfate-rich phase and at the phase boundary, whereas crystal growth was progressing mainly in the polyethylene glycol-rich phase. The crystals in the polyethylene glycol-rich phase grew to a size of >50 µm. Additionally, polyethylene glycol acted as an anti-solvent, thus, it influenced the crystallization yield. A phase diagram with an undersaturation zone, crystallization area, and amorphous precipitation zone was established. Only small differences in polyethylene glycol concentration caused significant shifts of the crystallization yield. An increase of the polyethylene glycol content from 2% (w/v) to 4% (w/v) increased the yield from approximately 63-87%, respectively. Our results show that crystallization in aqueous two-phase systems is an opportunity to foster process integration.
NASA Technical Reports Server (NTRS)
Karimi, Amir
1991-01-01
NASA's effort for the thermal environmental control of the Space Station Freedom is directed towards the design, analysis, and development of an Active Thermal Control System (ATCS). A two phase, flow through condenser/radiator concept was baselined, as a part of the ATCS, for the radiation of space station thermal load into space. The proposed condenser rejects heat through direct condensation of ATCS working fluid (ammonia) in the small diameter radiator tubes. Analysis of the condensation process and design of condenser tubes are based on the available two phase flow models for the prediction of flow regimes, heat transfer, and pressure drops. The prediction formulas use the existing empirical relationships of friction factor at gas-liquid interface. An attempt is made to study the stability of interfacial waves in two phase annular flow. The formulation is presented of a stability problem in cylindrical coordinates. The contribution of fluid viscosity, surface tension, and transverse radius of curvature to the interfacial surface is included. A solution is obtained for Kelvin-Helmholtz instability problem which can be used to determine the critical and most dangerous wavelengths for interfacial waves.
Simulation experiments for hot-leg U-bend two-phase flow phenomena
Ishii, M.; Hsu, J.T.; Tucholke, D.; Lambert, G.; Kataoka, I.
1986-01-01
In order to study the two-phase natural circulation and flow termination during a small break loss of coolant accident in LWR, simulation experiments have been performed. Based on the two-phase flow scaling criteria developed under this program, an adiabatic hot leg U-bend simulation loop using nitrogen gas and water and a Freon 113 boiling and condensation loop were built. The nitrogen-water system has been used to isolate key hydrodynamic phenomena from heat transfer problems, whereas the Freon loop has been used to study the effect of phase changes and fluid properties. Various tests were carried out to establish the basic mechanism of the flow termination and reestablishment as well as to obtain essential information on scale effects of parameters such as the loop frictional resistance, thermal center, U-bend curvature and inlet geometry. In addition to the above experimental study, a preliminary modeling study has been carried out for two-phase flow in a large vertical pipe at relatively low gas fluxes typical of natural circulation conditions.
A theory of electrophoresis of emulsion drops in aqueous two-phase polymer systems
NASA Technical Reports Server (NTRS)
Levine, S.
1982-01-01
An electrophoresis study has been carried out in an emulsion formed from an electrically neutral aqueous mixture of dextran and polyethylene glycol equilibrated at sufficient concentrations in the presence of electrolytes. Electrophoresis of a drop of one phase suspended in the other is observed, and the direction of the drop's motion is reversed when the disperse phase and the continuous phase are interchanged. In the presence of sulfate, phosphate, or citrate ions, an electrostatic potential difference of the order of a few mV exists between the two phases. The potential implied by the direction of the electrophoretic motion is opposite to the Donnan potential observed between the two phases. The mobility of an emulsion drop increases with the drop radius and depends on ion concentration. These results are explained in terms of a model postulating an electric dipole layer associated with a mixture of oriented polymer molecules at the surface of a drop, with a potential difference between the interiors of the two phases resulting from the unequal ion distribution.
Shadow imaging in bubbly gas-liquid two-phase flow in porous structures
NASA Astrophysics Data System (ADS)
Altheimer, Marco; Häfeli, Richard; Wälchli, Carmen; Rudolf von Rohr, Philipp
2015-09-01
Shadow imaging is used for the investigation of bubbly gas-liquid two-phase flow in a porous structure. The porous structure is made of Somos WaterShed XC 11122, a clear epoxy resin used in rapid prototyping. Optical access is provided by using an aqueous solution of sodium iodide and zinc iodide having the same refractive index as the structure material (). Nitrogen is injected into the continuous phase at volumetric transport fractions in the range of resulting in a hold-up of . The obtained images of overlapping bubble shadows are processed to measure the bubble dimensions. Therefore, a new processing sequence is developed to determine bubble dimensions from overlapping bubble shadows by ellipse fitting. The accuracy of the bubble detection and sizing routine is assessed processing synthetic images. It is shown that the developed technique is suitable for volumetric two-phase flow measurements. Important global quantities such as gas hold-up and total interfacial area can be measured with only one camera. Operation parameters for gas-liquid two-phase flows are determined to improve mass and heat transfer between the phases.
Two-phase PIV measurements of particle suspension in a forced impinging jet
NASA Astrophysics Data System (ADS)
Mulinti, Rahul; Kiger, Ken
2010-11-01
The condition of rotorcraft brownout is characterized by intense dust suspension that is uplifted during landing and takeoff operations in regions covered with loose sediment. To predict particle suspension and sedimentation within coupled particle-laden flows, detailed characterization of the micro-scale mechanics is needed within a prototypical flow that captures the essence of the rotorcraft/ground wake interactions. Two-phase PIV has been used to study the interaction of a sediment bed made of glass spheres with characteristic flow structures reminiscent from flow within a rotor wake. In order to make reliable simultaneous two-phase PIV measurements, a phase discrimination algorithm from a single two-phase image has been implemented. The validity of the separation is checked by processing images that consisted only of the very small tracer particles, or only the dispersed phase particles, and examining how much "cross-talk" was present between the phases. The mobilization and wall-normal flux of particulates by the vortex-wall interaction will be reported for several different operational conditions, and correlated to the local vortex conditions.
Gravitational instability in two-phase disks and the origin of the moon
NASA Technical Reports Server (NTRS)
Thompson, Christopher; Stevenson, David J.
1988-01-01
Two-phase disks may be gravitationally unstable at temperatures or surface densities at which a disk composed of either single phase would be highly stable. It is argued that two-phase disks can achieve a marginally unstable state (in addition to a highly unstable state that leads to fragmentation), limited by the ability of the photosphere to radiate the energy dissipated in the disk. A self-consistent prescription for the viscosity induced by the slow instabilities is provided. Two-phase disks are more centrally condensed than single-phase disks, and their secular cooling time may be comparable to their spreading time. A circumterrestrial disk of sufficient mass to form the moon provides a detailed example of all the preceding points. Its stability, structure, and dynamical evolution are investigated, and it is concluded that its spreading time is short (about 100 yr); the moon is formed molten, or partially molten; the moon's initial orbit lies in the earth's equatorial plane; and only a small fraction of the disk mass is lost in a wind, although this may represent a substantial fraction of volatiles. Most of these conclusions are independent of how the disk was formed, e.g., from a giant impact.
Fakhari, Abbas; Geier, Martin; Lee, Taehun
2016-06-15
typical chaotic structure in the flow field is observed at a Reynolds number of 10000, which indicates that the proposed model is a promising tool for direct numerical simulation of two-phase flows.
NASA Astrophysics Data System (ADS)
Fakhari, Abbas; Geier, Martin; Lee, Taehun
2016-06-01
typical chaotic structure in the flow field is observed at a Reynolds number of 10000, which indicates that the proposed model is a promising tool for direct numerical simulation of two-phase flows.
Methane metabolism in a stratified boreal lake
NASA Astrophysics Data System (ADS)
Nykänen, Hannu; Peura, Sari; Kankaala, Paula; Jones, Roger
2013-04-01
Stratified lakes, typical of the boreal zone, are naturally anoxic from their bottoms. In these lakes methanogenesis can account for up to half of organic matter degradation. However, a major part of the methane (CH4) is oxidized in the water column before reaching the atmosphere. Since methanotrophs use CH4 as their sole carbon and energy source, much CH4-derived carbon is incorporated into their biomass. Microbially produced CH4 has strongly negative δ13C compared to other carbon forms in ecosystems, making it possible to follow its route in food webs. However, only a few studies have estimated the amount of this microbial biomass or its carbon stable isotopic composition due to difficulties in separating it from other biomass or from other carbon forms in the water column. We estimated methanotrophic biomass from measured CH4 oxidation, and δ13C of the biomass from measured δ13C values of CH4, DIC, POM and DOC. An estimate of the fraction of methanotrophs in total microbial biomass is derived from bacterial community composition measurements. The study was made in, Alinen Mustajärvi, a small (area 0.75 ha, maximum depth 6.5 m, mean depth 4.2 m,), oligotrophic, mesohumic headwater lake located in boreal coniferous forest in southern Finland. CH4 and DIC concentrations and their δ13C were measured over the deepest point of the lake at 1 m intervals. 13C of DOM and POM were analyzed from composite samples from epi-, meta-, and hypolimnion. Evasion of CH4 and carbon dioxide from the lake surface to the atmosphere was estimated with boundary layer diffusion equations. CH4oxidation was estimated by comparing differences between observed concentrations and CH4potentially transported by turbulent diffusion between different vertical layers in the lake and also by actual methanotrophy measurements and from vertical differences in δ13C-CH4. The estimate of CH4 production was based on the sum of oxidized and released CH4. Molecular microbiology methods were used to
Using Nuclear Receptor Activity to Stratify Hepatocarcinogens
Shah, Imran; Houck, Keith; Judson, Richard S.; Kavlock, Robert J.; Martin, Matthew T.; Reif, David M.; Wambaugh, John; Dix, David J.
2011-01-01
utility of in vitro assays for stratifying environmental contaminants based on a combination of human bioactivity and rodent toxicity. PMID:21339822
Gas slug ascent through rheologically stratified conduits
NASA Astrophysics Data System (ADS)
Capponi, Antonio; James, Mike R.; Lane, Steve J.
2016-04-01
Textural and petrological evidence has indicated the presence of viscous, degassed magma layers at the top of the conduit at Stromboli. This layer acts as a plug through which gas slugs burst and it is thought to have a role in controlling the eruptive dynamics. Here, we present the results of laboratory experiments which detail the range of slug flow configurations that can develop in a rheologically stratified conduit. A gas slug can burst (1) after being fully accommodated within the plug volume, (2) whilst its base is still in the underlying low-viscosity liquid or (3) within a low-viscosity layer dynamically emplaced above the plug during the slug ascent. We illustrate the relevance of the same flow configurations at volcanic-scale through a new experimentally-validated 1D model and 3D computational fluid dynamic simulations. Applied to Stromboli, our results show that gas volume, plug thickness, plug viscosity and conduit radius control the transition between each configuration; in contrast, the configuration distribution seems insensitive to the viscosity of magma beneath the plug, which acts mainly to deliver the slug into the plug. Each identified flow configuration encompasses a variety of processes including dynamic narrowing and widening of the conduit, generation of instabilities along the falling liquid film, transient blockages of the slug path and slug break-up. All these complexities, in turn, lead to variations in the slug overpressure, mirrored by changes in infrasonic signatures which are also associated to different eruptive styles. Acoustic amplitudes are strongly dependent on the flow configuration in which the slugs burst, with both acoustic peak amplitudes and waveform shapes reflecting different burst dynamics. When compared to infrasonic signals from Stromboli, the similarity between real signals and laboratory waveforms suggests that the burst of a slug through a plug may represent a viable first-order mechanism for the generation of
Two-Phase Flow Simulations In a Natural Rock Fracture using the VOF Method
Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H., Bromhal, Grant
2010-01-01
Standard models of two-phase flow in porous media have been shown to exhibit several shortcomings that might be partially overcome with a recently developed model based on thermodynamic principles (Hassanizadeh and Gray, 1990). This alternative two-phase flow model contains a set of new and non-standard parameters, including specific interfacial area. By incorporating interfacial area production, destruction, and propagation into functional relationships that describe the capillary pressure and saturation, a more physical model has been developed. Niessner and Hassanizadeh (2008) have examined this model numerically and have shown that the model captures saturation hysteresis with drainage/imbibition cycles. Several static experimental studies have been performed to examine the validity of this new thermodynamically based approach; these allow the determination of static parameters of the model. To date, no experimental studies have obtained information about the dynamic parameters required for the model. A new experimental porous flow cell has been constructed using stereolithography to study two-phase flow phenomena (Crandall et al. 2008). A novel image analysis tool was developed for an examination of the evolution of flow patterns during displacement experiments (Crandall et al. 2009). This analysis tool enables the direct quantification of interfacial area between fluids by matching known geometrical properties of the constructed flow cell with locations identified as interfaces from images of flowing fluids. Numerous images were obtained from two-phase experiments within the flow cell. The dynamic evolution of the fluid distribution and the fluid-fluid interface locations were determined by analyzing these images. In this paper, we give a brief introduction to the thermodynamically based two-phase flow model, review the properties of the stereolithography flow cell, and show how the image analysis procedure has been used to obtain dynamic parameters for the
Cai, Y.; Wambsganss, M.W.; Jendrzejczyk, J.A.
1996-02-01
Various measurement tools of chaos theory were applied to analyze two-phase pressure signals with the objective to identify and interpret flow pattern transitions for two-phase flows in a small, horizontal rectangular channel. These measurement tools included power spectral density function, autocorrelation function, pseudo-phase-plane trajectory, Lyapunov exponents, and fractal dimensions. It was demonstrated that the randomlike pressure fluctuations characteristic of two-phase flow in small rectangular channels are chaotic in nature. As such, they are governed by a high-order deterministic system. The correlation dimension is potentially a new approach for identification of certain two-phase flow patterns and transitions.
NASA Astrophysics Data System (ADS)
Burkholder, Michael B.; Litster, Shawn
2016-05-01
In this study, we analyze the stability of two-phase flow regimes and their transitions using chaotic and fractal statistics, and we report new measurements of dynamic two-phase pressure drop hysteresis that is related to flow regime stability and channel water content. Two-phase flow dynamics are relevant to a variety of real-world systems, and quantifying transient two-phase flow phenomena is important for efficient design. We recorded two-phase (air and water) pressure drops and flow images in a microchannel under both steady and transient conditions. Using Lyapunov exponents and Hurst exponents to characterize the steady-state pressure fluctuations, we develop a new, measurable regime identification criteria based on the dynamic stability of the two-phase pressure signal. We also applied a new experimental technique by continuously cycling the air flow rate to study dynamic hysteresis in two-phase pressure drops, which is separate from steady-state hysteresis and can be used to understand two-phase flow development time scales. Using recorded images of the two-phase flow, we show that the capacitive dynamic hysteresis is related to channel water content and flow regime stability. The mixed-wettability microchannel and in-channel water introduction used in this study simulate a polymer electrolyte fuel cell cathode air flow channel.
Design Manual for Microgravity Two-Phase Flow and Heat Transfer
1989-10-01
xi/xii NOMENCLATURE Symbol Description Units a magnitude of acceleration vector (mis 2) A cross-sectional area of flow channel or radiator surface ( M 2...Pa/ m ) (dP/dz) f frictional pressure gradient (Pa/ m ) (dP/dz)g pressure gradient due to body forces (Pa/ m ) (dP/dz) total pressure gradient (Pa/ m ) D...diameter of pipe ir) Dg* dimensionless hydraulic diameter for gas phase in stratified flow Dh hydraulic diameter in heated (evaporator) tube ( m ) D1
Role of Nucleation and Growth in Two-Phase Microstructure Formation
Shin, Jong Ho
2007-01-01
During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different
Zhang, G; Stillinger, F H; Torquato, S
2016-12-28
Disordered hyperuniform many-particle systems have attracted considerable recent attention, since they behave like crystals in the manner in which they suppress large-scale density fluctuations, and yet also resemble statistically isotropic liquids and glasses with no Bragg peaks. One important class of such systems is the classical ground states of "stealthy potentials." The degree of order of such ground states depends on a tuning parameter χ. Previous studies have shown that these ground-state point configurations can be counterintuitively disordered, infinitely degenerate, and endowed with novel physical properties (e.g., negative thermal expansion behavior). In this paper, we focus on the disordered regime (0 < χ < 1/2) in which there is no long-range order and control the degree of short-range order. We map these stealthy disordered hyperuniform point configurations to two-phase media by circumscribing each point with a possibly overlapping sphere of a common radius a: the "particle" and "void" phases are taken to be the space interior and exterior to the spheres, respectively. The hyperuniformity of such two-phase media depends on the sphere sizes: While it was previously analytically proven that the resulting two-phase media maintain hyperuniformity if spheres do not overlap, here we show numerically that they lose hyperuniformity whenever the spheres overlap. We study certain transport properties of these systems, including the effective diffusion coefficient of point particles diffusing in the void phase as well as static and time-dependent characteristics associated with diffusion-controlled reactions. Besides these effective transport properties, we also investigate several related structural properties, including pore-size functions, quantizer error, an order metric, and percolation thresholds. We show that these transport, geometrical, and topological properties of our two-phase media derived from decorated stealthy ground states are distinctly
Modelling Air and Water Two-Phase Annular Flow in a Small Horizontal Pipe
NASA Astrophysics Data System (ADS)
Yao, Jun; Yao, Yufeng; Arini, Antonino; McIiwain, Stuart; Gordon, Timothy
2016-06-01
Numerical simulation using computational fluid dynamics (CFD) has been carried out to study air and water two-phase flow in a small horizontal pipe of an inner diameter of 8.8mm, in order to investigate unsteady flow pattern transition behaviours and underlying physical mechanisms. The surface liquid film thickness distributions, determined by either wavy or full annular flow regime, are shown in reasonable good agreement with available experimental data. It was demonstrated that CFD simulation was able to predict wavy flow structures accurately using two-phase flow sub-models embedded in ANSYS-Fluent solver of Eulerian-Eulerian framework, together with a user defined function subroutine ANWAVER-UDF. The flow transient behaviours from bubbly to annular flow patterns and the liquid film distributions revealed the presence of gas/liquid interferences between air and water film interface. An increase of upper wall liquid film thickness along the pipe was observed for both wavy annular and full annular scenarios. It was found that the liquid wavy front can be further broken down to form the water moisture with liquid droplets penetrating upwards. There are discrepancies between CFD predictions and experimental data on the liquid film thickness determined at the bottom and the upper wall surfaces, and the obtained modelling information can be used to assist further 3D user defined function subroutine development, especially when CFD simulation becomes much more expense to model full 3D two-phase flow transient performance from a wavy annular to a fully developed annular type.
NASA Astrophysics Data System (ADS)
Goto, H.; Aichi, M.; Tokunaga, T.; Yamamoto, H.; Ogawa, T.; Aoki, T.
2013-12-01
Coupled two-phase fluid flow and deformation of Berea sandstone was discussed through laboratory experiments and numerical simulation. In the experiment, a triaxial compression apparatus with flow pipes to pass fluids through a rock sample was used. The experimental procedures were as follows. Firstly, external stresses close to hydrostatic condition were applied to a water saturated cylindrical Berea sandstone sample. Then, compressed air was infiltrated from the bottom of the sample. During the experiment, both axial and circumferential strains at half the height of the sample and volumetric discharge of water at the outlet were measured. Both strains showed sudden extensions after a few seconds, and monotonically extended thereafter. The volumetric discharge of water showed that air breakthrough occurred in around 100 seconds after the commencement of the air injection. Numerical simulations based on thermodynamically consistent constitutive equations were conducted in order to quantitatively analyze the experimental results. In a simulation in which the material was assumed to be homogeneous isotropic, the axial strain at half the height of the sample and the volumetric discharge of water at the outlet were reproduced well by using reasonable parameters, while that was not the case with the circumferential strain at half the height of the sample. On the other hand, in a simulation in which anisotropy of the material was introduced, all experimental data were reproduced well by using reasonable parameters. This result is reasonable because Berea sandstone is well known to be anisotropic under such Terzaghi effective stress condition as used in our experiment, i.e., 3.0 MPa (Hart and Wang, 1999; Hart, 2000). Our results indicate that the theory of poroelasticity for two-phase fluid system can explain the strain behavior of porous media for two-phase fluid flow observed in laboratory experiments.
Waves, Instabilities, and Rivulets in High Quality Microgap Two-Phase Flow
NASA Astrophysics Data System (ADS)
Bar-Cohen, A.; Holloway, C.
2016-09-01
Two-phase flow in sub-millimeter microgap channels offers highly potent thermal management capability and is the foundation for the emerging "embedded cooling" paradigm of electronic cooling. While the thermofluid characteristics and operational limits of such microcoolers are intimately tied to distinct forms of vapor-liquid aggregation in the microgap channel, insufficient attention has been paid to the formation of distinct wave patterns and instabilities on the thin liquid films associated with high-quality microgap channel flow. This paper focuses on the results of visualization and heat transfer studies of such two-phase flows, under both adiabatic and diabatic conditions, for FC-72 flowing in a 184 micron microgap channel at a mass flux of 230 kg/(m2.s). The study has revealed the existence of a post-annular, high-quality Rivulet flow regime, in which the liquid film breakdown and local wall dryout drives large surface anisothermalities and limits the heat transfer rate from the wall. As predicted by the prevailing flow regime models, annular flow is found to be the dominant flow regime for this microgap configuration.. For the adiabatic conditions, flow qualities ranged between 27% and 81%, and widely spaced, 3D waves, with a wavelength that decreases with increasing flow quality, were observed on the liquid-vapor interface. For the diabatic condition, the inlet flow quality was maintained at 36% and the exit flow quality varied between 47% and 97%. For exit qualities greater than 61%, the liquid film would periodically rupture into rivulet of varying width and length. The spacing, length, and width of the rivulets varied considerably, and can easily stretch well into dryout region. The axial variation of the wall heat transfer coefficient was found to reflect and confirm the expected axial propagation of the two- phase flow regimes and the onset of local dryout associated with the newly-defined Rivulet regime.
Advanced numerical methods for three dimensional two-phase flow calculations
Toumi, I.; Caruge, D.
1997-07-01
This paper is devoted to new numerical methods developed for both one and three dimensional two-phase flow calculations. These methods are finite volume numerical methods and are based on the use of Approximate Riemann Solvers concepts to define convective fluxes versus mean cell quantities. The first part of the paper presents the numerical method for a one dimensional hyperbolic two-fluid model including differential terms as added mass and interface pressure. This numerical solution scheme makes use of the Riemann problem solution to define backward and forward differencing to approximate spatial derivatives. The construction of this approximate Riemann solver uses an extension of Roe`s method that has been successfully used to solve gas dynamic equations. As far as the two-fluid model is hyperbolic, this numerical method seems very efficient for the numerical solution of two-phase flow problems. The scheme was applied both to shock tube problems and to standard tests for two-fluid computer codes. The second part describes the numerical method in the three dimensional case. The authors discuss also some improvements performed to obtain a fully implicit solution method that provides fast running steady state calculations. Such a scheme is not implemented in a thermal-hydraulic computer code devoted to 3-D steady-state and transient computations. Some results obtained for Pressurised Water Reactors concerning upper plenum calculations and a steady state flow in the core with rod bow effect evaluation are presented. In practice these new numerical methods have proved to be stable on non staggered grids and capable of generating accurate non oscillating solutions for two-phase flow calculations.
Design of a Subscale Propellant Slag Evaluation Motor Using Two-Phase Fluid Dynamic Analysis
NASA Technical Reports Server (NTRS)
Whitesides, R. Harold; Dill, Richard A.; Purinton, David C.; Sambamurthi, Jay K.
1996-01-01
Small pressure perturbations in the Space Shuttle Reusable Solid Rocket Motor (RSRM) are caused by the periodic expulsion of molten aluminum oxide slag from a pool that collects in the aft end of the motor around the submerged nozzle nose during the last half of motor operation. It is suspected that some motors produce more slag than others due to differences in aluminum oxide agglomerate particle sizes that may relate to subtle differences in propellant ingredient characteristics such as particle size distributions or processing variations. A subscale motor experiment was designed to determine the effect of propellant ingredient characteristics on the propensity for slag production. An existing 5 inch ballistic test motor was selected as the basic test vehicle. The standard converging/diverging nozzle was replaced with a submerged nose nozzle design to provide a positive trap for the slag that would increase the measured slag weights. Two-phase fluid dynamic analyses were performed to develop a nozzle nose design that maintained similitude in major flow field features with the full scale RSRM. The 5 inch motor was spun about its longitudinal axis to further enhance slag collection and retention. Two-phase flow analysis was used to select an appropriate spin rate along with other considerations, such as avoiding bum rate increases due to radial acceleration effects. Aluminum oxide particle distributions used in the flow analyses were measured in a quench bomb for RSRM type propellants with minor variations in ingredient characteristics. Detailed predictions for slag accumulation weights during motor bum compared favorably with slag weight data taken from defined zones in the subscale motor and nozzle. The use of two-phase flow analysis proved successful in gauging the viability of the experimental program during the planning phase and in guiding the design of the critical submerged nose nozzle.
Characterization and comparative profiling of the small RNA transcriptomes in two phases of locust
Wei, Yuanyuan; Chen, Shuang; Yang, Pengcheng; Ma, Zongyuan; Kang, Le
2009-01-01
Background All the reports on insect small RNAs come from holometabolous insects whose genome sequence data are available. Therefore, study of hemimetabolous insect small RNAs could provide more insights into evolution and function of small RNAs in insects. The locust is an important, economically harmful hemimetabolous insect. Its phase changes, as a phenotypic plasticity, result from differential gene expression potentially regulated at both the post-transcriptional level, mediated by small RNAs, and the transcriptional level. Results Here, using high-throughput sequencing, we characterize the small RNA transcriptome in the locust. We identified 50 conserved microRNA families by similarity searching against miRBase, and a maximum of 185 potential locust-specific microRNA family candidates were identified using our newly developed method independent of locust genome sequence. We also demonstrate conservation of microRNA*, and evolutionary analysis of locust microRNAs indicates that the generation of miRNAs in locusts is concentrated along three phylogenetic tree branches: bilaterians, coelomates, and insects. Our study identified thousands of endogenous small interfering RNAs, some of which were of transposon origin, and also detected many Piwi-interacting RNA-like small RNAs. Comparison of small RNA expression patterns of the two phases showed that longer small RNAs were expressed more abundantly in the solitary phase and that each category of small RNAs exhibited different expression profiles between the two phases. Conclusions The abundance of small RNAs in the locust might indicate a long evolutionary history of post-transcriptional gene expression regulation, and differential expression of small RNAs between the two phases might further disclose the molecular mechanism of phase changes. PMID:19146710
Disturbed zone effects: Two phase flow in regionally water-saturated fractured rock
Geller, J.T.; Doughty, C.; Long, J.C.S.
1995-01-01
Field evidence suggests that two-phase flow may develop near underground excavations in regionally-saturated fractured crystalline rock, resulting in lower inflow rates compared to undisturbed rock. Mechanisms for the development of two-phase flow conditions include depressurization of formation water that is supersaturated with dissolved gas and buoyancy-driven air invasion into fractures from the drift. Models that assume gas-liquid phase equilibrium indicate that for constant head boundary conditions, the build-up of pressure behind the gas phase evolving from depressurization should redissolve the gas and maintain higher flowrates, requiring unreasonably high dissolved gas concentrations to produce observed flow reductions at the Stripa Mine in Sweden. This discrepancy initiated a laboratory-scale investigation. Gas evolution following depressurization is simulated in two different 8 cm x 8 cm transparent fracture replicas for linear flow with constant head boundary conditions. Gas forms and accumulates in the large apertures and the extent of flow reduction is greater when the flow through the fracture is controlled by a large aperture channel, compared to a fracture where large aperture regions are relatively isolated. An effective continuum numerical model (TOUGH2) is used to describe the development of two-phase flow under degassing conditions. Numerical simulations were made for a homogeneous porous medium and for a heterogeneous medium using the aperture distribution of one of the fractures used in the laboratory experiments, which allows a direct comparison between laboratory and numerical results. The incorporation of kinetic expressions into the numerical model will allow the prediction of resaturation rates of a repository following closure.
Design and construction of an experiment for two-phase flow in fractured porous media
Ayala, R.E.G.; Aziz, K.
1993-08-01
In numerical reservoir simulation naturally fractured reservoirs are commonly divided into matrix and fracture systems. The high permeability fractures are usually entirely responsible for flow between blocks and flow to the wells. The flow in these fractures is modeled using Darcy`s law and its extension to multiphase flow by means of relative permeabilities. The influence and measurement of fracture relative permeability for two-phase flow in fractured porous media have not been studied extensively, and the few works presented in the literature are contradictory. Experimental and numerical work on two-phase flow in fractured porous media has been initiated. An apparatus for monitoring this type of flow was designed and constructed. It consists of an artificially fractured core inside an epoxy core holder, detailed pressure and effluent monitoring, saturation measurements by means of a CT-scanner and a computerized data acquisition system. The complete apparatus was assembled and tested at conditions similar to the conditions expected for the two-phase flow experiments. Fine grid simulations of the experimental setup-were performed in order to establish experimental conditions and to study the effects of several key variables. These variables include fracture relative permeability and fracture capillary pressure. The numerical computations show that the flow is dominated by capillary imbibition, and that fracture relative permeabilities have only a minor influence. High oil recoveries without water production are achieved due to effective water imbibition from the fracture to the matrix. When imbibition is absent, fracture relative permeabilities affect the flow behavior at early production times.
A Non-Fickian Mixing Model for Stratified Turbulent Flows
2011-09-30
1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. A Non-Fickian Mixing Model for Stratified Turbulent Flows...would be to improve the predictive skill of the Navy numerical models for submesoscale transport in the ocean. OBJECTIVES My main objective...COVERED 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE A Non-Fickian Mixing Model for Stratified Turbulent Flows 5a. CONTRACT NUMBER 5b. GRANT
Digital phase conjugate mirror by parallel arrangement of two phase-only spatial light modulators.
Shibukawa, Atsushi; Okamoto, Atsushi; Goto, Yuta; Honma, Satoshi; Tomita, Akihisa
2014-05-19
In a conventional digital phase conjugation system, only the phase of an input light is time-reversed. This deteriorates phase conjugation fidelity and restricts application fields to specific cases only when the input light has uniformly-distributed scattered wavefront. To overcome these difficulties, we present a digital phase conjugate mirror based on parallel alignment of two phase-only spatial light modulators (SLMs), in which both amplitude and phase of the input light can be time-reversed. Experimental result showed that, in the phase conjugation through a holographic diffuser with diffusion angle of 0.5 degree, background noises decrease to 65% by our digital phase conjugation mirror.
Identification of microfluidic two-phase flow patterns in lab-on-chip devices.
Yang, Zhaochu; Dong, Tao; Halvorsen, Einar
2014-01-01
This work describes a capacitive sensor for identification of microfluidic two-phase flow in lab-on-chip devices. With interdigital electrodes and thin insulation layer utilized, this sensor is capable of being integrated with the microsystems easily. Transducing principle and design considerations are presented with respect to the microfluidic gas/liquid flow patterns. Numerical simulation results verify the operational principle. And the factors affecting the performance of the sensor are discussed. Besides, a feasible process flow for the fabrication is also proposed.
A Two-Phase Solid/Fluid Model for Dense Granular Flows Including Dilatancy Effects
NASA Astrophysics Data System (ADS)
Mangeney, A.; Bouchut, F.; Fernández-Nieto, E. D.; Narbona-Reina, G.; Kone, E. H.
2014-12-01
We propose a thin layer depth-averaged two-phase model to describe solid-fluid mixtures such as debris flows. It describes the velocity of the two phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure, that itself modifies the friction within the granular phase (Iverson et al., 2010). The model is derived from a 3D two-phase model proposed by Jackson (2000) based on the 4 equations of mass and momentum conservation within the two phases. This system has 5 unknowns: the solid and fluid velocities, the solid and fluid pressures and the solid volume fraction. As a result, an additional equation inside the mixture is necessary to close the system. Surprisingly, this issue is inadequately accounted for in the models that have been developed on the basis of Jackson's work (Bouchut et al., 2014). In particular, Pitman and Le replaced this closure simply by imposing an extra boundary condition at the surface of the flow. When making a shallow expansion, this condition can be considered as a closure condition. However, the corresponding model cannot account for a dissipative energy balance. We propose here an approach to correctly deal with the thermodynamics of Jackson's equations. We close the mixture equations by a weak compressibility relation involving a critical density, or equivalently a critical pressure. Moreover, we relax one boundary condition, making it possible for the fluid to escape the granular media when compression of the granular mass occurs. Furthermore, we introduce second order terms in the equations making it possible to describe the evolution of the pore fluid pressure in response to the compression/dilatation of the granular mass without prescribing an extra ad-hoc equation for the pore pressure. We prove that the energy balance associated with this Jackson closure is dissipative, as well as its thin layer associated model. We present several numerical tests for the 1D case that are compared to the
Numerical modeling of two-phase behavior in the PEFC gas diffusion layer
Mukherjee, Partha Pa223876; Kang, Qinjun; Mukundan, Rangachary; Borup, Rod L
2009-01-01
A critical performance limitation in the polymer electrolye fuel cell (PEFC) is attributed to the mass transport loss originating from suboptimal liquid water transport and flooding phenomena. Liquid water can block the porous pathways in the fibrous gas diffusion layer (GDL) and the catalyst layer (CL), thus hindering oxygen transport from the flow field to the electrochemically actives sites in the catalyst layer. In this paper, the study of the two phase behavior and the durability implications due to the wetting characteristics in the carbon paper GDL are presented using a pore-scale modeling framework.
Ensemble distribution for immiscible two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Savani, Isha; Bedeaux, Dick; Kjelstrup, Signe; Vassvik, Morten; Sinha, Santanu; Hansen, Alex
2017-02-01
We construct an ensemble distribution to describe steady immiscible two-phase flow of two incompressible fluids in a porous medium. The system is found to be ergodic. The distribution is used to compute macroscopic flow parameters. In particular, we find an expression for the overall mobility of the system from the ensemble distribution. The entropy production at the scale of the porous medium is shown to give the expected product of the average flow and its driving force, obtained from a black-box description. We test numerically some of the central theoretical results.
A general microwave-assisted two-phase strategy for nanocrystals synthesis.
Li, Yizhao; Yang, Chao; Ge, Jianhua; Sun, Chao; Wang, Jide; Su, Xintai
2013-10-01
A general microwave-assisted two-phase strategy (MTS) has been developed for the synthesis of monodisperse inorganic nanocrystals (NCs). A series of metal oxides, ferrite, hydroxides, and metal sulfide NCs were synthesized by using water-soluble metal salts. The obtained NCs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The composition, size, and shape of the NCs can be tuned by the types of precursors, the concentrations of metal ions, and the species of ligands. This protocol creates a new synthetic route, which may also be further extended to synthesize other nanomaterials, including alloy, noble metal, rare-earth fluorescent, etc.
Electrical impedance imaging in two-phase, gas-liquid flows: 1. Initial investigation
NASA Technical Reports Server (NTRS)
Lin, J. T.; Ovacik, L.; Jones, O. C.
1991-01-01
The determination of interfacial area density in two-phase, gas-liquid flows is one of the major elements impeding significant development of predictive tools based on the two-fluid model. Currently, these models require coupling of liquid and vapor at interfaces using constitutive equations which do not exist in any but the most rudimentary form. Work described herein represents the first step towards the development of Electrical Impedance Computed Tomography (EICT) for nonintrusive determination of interfacial structure and evolution in such flows.
Fractionation of wheat gliadins by counter-current distribution using an organic two-phase system.
Truust, H; Johansson, G
1998-06-26
A liquid liquid two-phase system based on N,N-dimethylformamide and the two polymers, poly(ethyleneglycol) and Ficoll, useful for partitioning of hydrophobic proteins, has been developed. The system has been applied to a counter-current distribution process in 56 steps for analysing the heterogeneity of proteins extracted with N,N-dimethylformamide from wheat flour. The counter-current distribution patterns of proteins, extracted from eight kinds of wheat, have been analysed. The minimum number of hypothetical proteins necessary to describe the patterns was found to be seven. The relative amount of these hypothetical components varied among the wheats.
High-yield isolation of extracellular vesicles using aqueous two-phase system
Shin, Hyunwoo; Han, Chungmin; Labuz, Joseph M.; Kim, Jiyoon; Kim, Jongmin; Cho, Siwoo; Gho, Yong Song; Takayama, Shuichi; Park, Jaesung
2015-01-01
Extracellular vesicles (EVs) such as exosomes and microvesicles released from cells are potential biomarkers for blood-based diagnostic applications. To exploit EVs as diagnostic biomarkers, an effective pre-analytical process is necessary. However, recent studies performed with blood-borne EVs have been hindered by the lack of effective purification strategies. In this study, an efficient EV isolation method was developed by using polyethylene glycol/dextran aqueous two phase system (ATPS). This method provides high EV recovery efficiency (~70%) in a short time (~15 min). Consequently, it can significantly increase the diagnostic applicability of EVs. PMID:26271727
An exact solution of a simplified two-phase plume model. [for solid propellant rocket
NASA Technical Reports Server (NTRS)
Wang, S.-Y.; Roberts, B. B.
1974-01-01
An exact solution of a simplified two-phase, gas-particle, rocket exhaust plume model is presented. It may be used to make the upper-bound estimation of the heat flux and pressure loads due to particle impingement on the objects existing in the rocket exhaust plume. By including the correction factors to be determined experimentally, the present technique will provide realistic data concerning the heat and aerodynamic loads on these objects for design purposes. Excellent agreement in trend between the best available computer solution and the present exact solution is shown.
Decay of the 3D viscous liquid-gas two-phase flow model with damping
NASA Astrophysics Data System (ADS)
Zhang, Yinghui
2016-08-01
We establish the optimal Lp - L2(1 ≤ p < 6/5) time decay rates of the solution to the Cauchy problem for the 3D viscous liquid-gas two-phase flow model with damping and analyse the influences of the damping on the qualitative behaviors of solution. It is observed that the fraction effect of the damping affects the dispersion of fluids and enhances the time decay rate of solution. Our method of proof consists of Hodge decomposition technique, Lp - L2 estimates for the linearized equations, and delicate energy estimates.
Statistics of light deflection in a random two-phase medium
Sviridov, A P
2007-01-31
The statistics of the angles of light deflection during its propagation in a random two-phase medium with randomly oriented phase interfaces is considered within the framework of geometrical optics. The probabilities of finding a randomly walking photon in different phases of the inhomogeneous medium are calculated. Analytic expressions are obtained for the scattering phase function and the scattering phase matrix which relates the Stokes vector of the incident light beam with the Stokes vectors of deflected beams. (special issue devoted to multiple radiation scattering in random media)
Molino, João Vitor Dutra; Viana Marques, Daniela de Araújo; Júnior, Adalberto Pessoa; Mazzola, Priscila Gava; Gatti, Maria Silvia Viccari
2013-01-01
Upstream improvements have led to significant advances in the productivity of biomolecules and bioparticles. Today, downstream processes are the bottleneck in the production of some biopharmaceuticals, a change from previous years. Current purification platforms will reach their physical limits at some point, indicating the need for new approaches. This article reviews an alternative method to extract and purify biomolecules/bioparticles named aqueous two-phase system (ATPS). Biocompatibility and readiness to scale up are some of the ATPS characteristics. We also discuss some of ATPS applications in the biotechnology field.
Solution and precipitation hardening in carbon-doped two-phase {gamma}-titanium aluminides
Appel, F.; Christoph, U.; Wagner, R.
1997-12-31
A two-phase titanium aluminide alloy was systematically doped with carbon to improve its high temperature strength. Solid solutions and precipitates of carbon were formed by different thermal treatments. A fine dispersion of perovskite precipitates was found to be very effective for improving the high temperature strength and creep resistance of the material. The strengthening mechanisms were characterized by flow stresses and activation parameters. The investigations were accompanied by electron microscope observation of the defect structure which was generated during deformation. Special attention was paid on the interaction mechanisms of perfect and twinning dislocations with the carbide precipitates.
Measurement and prediction of two-phase flow patterns for new refrigerants inside horizontal tubes
Kattan, N.; Favrat, D.; Thome, J.R.
1995-12-31
Two-phase flow pattern data were obtained with 12-mm-bore sight glasses for five refrigerants: R-123, R-134a, R-502, R-402A, and R-404A. The existing flow pattern maps of Taitel and Dukler (1976) and Hashizume (1983) poorly represented the data, while, with the exception of mist flows, the VDI map identified the flow patterns successfully. Methods used in horizontal flow boiling correlations to determine the threshold between all wet wall and partially wet wall flows were shown to be unreliable.
Wither the Jasmine: China’s Two-Phase Operation for Cyber Control-in-Depth
2012-01-01
35 Wither the Jasmine China’s Two-Phase Operation for Cyber Control-in-Depth Scott J. HenderSon* China’s Jasmine Revolution, an online movement that...mundane death. A passive shrug of the shoulders, and the embryonic movement withered and died on the vine. Some would argue that the Jasmine Revolution...revolution, and it was not a serious movement. These and a host of other reasons explain the Jasmine Revolution’s untimely demise. Whether the result of one
Method and turbine for extracting kinetic energy from a stream of two-phase fluid
NASA Technical Reports Server (NTRS)
Elliott, D. G. (Inventor)
1979-01-01
An axial flow separator turbine is described which includes a number of nozzles for delivering streams of a two-phase fluid along linear paths. A phase separator which responsively separates the vapor and liquid is characterized by concentrically related annuli supported for rotation within the paths. The separator has endless channels for confining the liquid under the influence of centrifugal forces. A vapor turbine fan extracts kinetic energy from the liquid. Angular momentum of both the liquid phase and the vapor phase of the fluid is converted to torque.
Pressure Profiles in Two-Phase Geothermal Wells: Comparison of Field Data and Model Calculations
Ambastha, A.K.; Gudmundsson, J.S.
1986-01-21
Increased confidence in the predictive power of two-phase correlations is a vital part of wellbore deliverability and deposition studies for geothermal wells. Previously, the Orkiszewski (1967) set of correlations has been recommended by many investigators to analyze geothermal wellbore performance. In this study, we use measured flowing pressure profile data from ten geothermal wells around the world, covering a wide range of flowrate, fluid enthalpy, wellhead pressure and well depth. We compare measured and calculated pressure profiles using the Orkiszewski (1967) correlations.
Morphology and Magnetic Properties of Ferriferous Two-Phase Sodium Borosilicate Glasses
Naberezhnov, Alexander; Porechnaya, Nadezda; Nizhankovskii, Viktor; Filimonov, Alexey; Nacke, Bernard
2014-01-01
This contribution is devoted to the study of morphology and magnetic properties of sodium borosilicate glasses with different concentrations (15, 20, and 25 wt.%) of α-Fe2O3 in an initial furnace charge. These glasses were prepared by a melt-quenching method. For all glasses a coexistence of drop-like and two-phase interpenetrative structures is observed. The most part of a drop structure is formed by self-assembling iron oxides particles. All types of glasses demonstrate the magnetic properties and can be used for preparation of porous magnetic matrices with nanometer through dendrite channel structure. PMID:25162045
Prediction of gas-liquid two-phase flow regime in microgravity
NASA Technical Reports Server (NTRS)
Lee, Jinho; Platt, Jonathan A.
1993-01-01
An attempt is made to predict gas-liquid two-phase flow regime in a pipe in a microgravity environment through scaling analysis based on dominant physical mechanisms. Simple inlet geometry is adopted in the analysis to see the effect of inlet configuration on flow regime transitions. Comparison of the prediction with the existing experimental data shows good agreement, though more work is required to better define some physical parameters. The analysis clarifies much of the physics involved in this problem and can be applied to other configurations.
Two-Phase Nozzle Theory and Parametric Analysis. Phase II. Parametric Analysis and Optimization.
1981-07-01
Dekker, Inc., 1969. 4. Netzer, D . W.: Calculations of Flow Characteristics for Two-Phase Flow in Annular Converging-Diverging Nozzles. Report No. TM-62-3...Astronautica Acta, Vol. 11, No. 3, pp. 207-216, 1965. 6. Crowe, C. T., M. P. Sharma and D . E. Stock: The Particle-Source-In Cell (PSI-Cell) Model for...Dispersed Droplet-in-Vapor Flows Including Normal Shock Waves. ASME J. of Fluids Eng’g., pp. 355-362, 1978. 8. Elliott, D . G.: "Theoretical and
Two-Phase Flow Research on the ISS for Thermal Control Applications
NASA Technical Reports Server (NTRS)
Motil, Brian J.
2013-01-01
With the era of full utilization of the ISS now upon us, this presentation will discuss some of the highest-priority areas for two-phase flow systems with thermal control applications. These priorities are guided by recommendations of a 2011 NRC Decadal Survey report, Recapturing a Future for Space Exploration, Life and Physical Sciences for a New Era as well as an internal NASA exercise in response to the NRC report conducted in early 2012. Many of these proposals are already in various stages of development, while others are still conceptual.
Computation of Space Shuttle high-pressure cryogenic turbopump ball bearing two-phase coolant flow
NASA Technical Reports Server (NTRS)
Chen, Yen-Sen
1990-01-01
A homogeneous two-phase fluid flow model, implemented in a three-dimensional Navier-Stokes solver using computational fluid dynamics methodology is described. The application of the model to the analysis of the pump-end bearing coolant flow of the high-pressure oxygen turbopump of the Space Shuttle main engine is studied. Results indicate large boiling zones and hot spots near the ball/race contact points. The extent of the phase change of the liquid oxygen coolant flow due to the frictional and viscous heat fluxes near the contact areas has been investigated for the given inlet conditions of the coolant.
Two phase flow and heat transfer in porous beds under variable body forces, part 2
NASA Technical Reports Server (NTRS)
Evers, J. L.; Henry, H. R.
1969-01-01
Analytical and experimental investigations of a pilot model of a channel for the study of two-phase flow under low or zero gravity are presented. The formulation of dimensionless parameters to indicate the relative magnitude of the effects of capillarity, gravity, pressure gradient, viscosity, and inertia is described. The investigation is based on the principal equations of fluid mechanics and thermodynamics. Techniques were investigated by using a laser velocimeter for measuring point velocities of the fluid within the porous material without disturbing the flow.
Two-Phase Cryogenic Heat Exchanger for the Thermodynamic Vent System
NASA Technical Reports Server (NTRS)
Christie, Robert J.
2011-01-01
A two-phase cryogenic heat exchanger for a thermodynamic vent system was designed and analyzed, and the predicted performance was compared with test results. A method for determining the required size of the Joule-Thomson device was also developed. Numerous sensitivity studies were performed to show that the design was robust and possessed a comfortable capacity margin. The comparison with the test results showed very similar heat extraction performance for similar inlet conditions. It was also shown that estimates for Joule- Thomson device flow rates and exit quality can vary significantly and these need to be accommodated for with a robust system design.
Working fluid selection for space-based two-phase heat transport systems
NASA Technical Reports Server (NTRS)
Mclinden, Mark O.
1988-01-01
The working fluid for externally-mounted, space-based two-phase heat transport systems is considered. A sequence of screening criteria involving freezing and critical point temperatures and latent heat of vaporization and vapor density are applied to a data base of 860 fluids. The thermal performance of the 52 fluids which pass this preliminary screening are then ranked according to their impact on the weight of a reference system. Upon considering other nonthermal criteria (flammability, toxicity, and chemical stability) a final set of 10 preferred fluids is obtained. The effects of variations in system parameters is investigated for these 10 fluids by means of a factorial design.
Two-phase treatment of patients with crossbite and tendency toward skeletal Class III malocclusion*
Bayerl, Maria de Lourdes Machado
2014-01-01
Angle Class III malocclusion is characterized by an inadequate anteroposterior dental relationship which may or may not be accompanied by skeletal changes. In general, patients are distressed by a significantly compromised facial aspect which, when associated with a deficient middle third, encourages patients to seek treatment. This article reports a two-phase treatment carried out in a female patient aged six years and six months with a tendency towards a Class III skeletal pattern. This case was presented to the Brazilian Board of Orthodontics and Facial Orthopedics (BBO). It is representative of the Discrepancy Index (DI) category, and fulfills part of the requirements for obtaining BBO Diploma. PMID:25279531
Two phase sampling for wheat acreage estimation. [large area crop inventory experiment
NASA Technical Reports Server (NTRS)
Thomas, R. W.; Hay, C. M.
1977-01-01
A two phase LANDSAT-based sample allocation and wheat proportion estimation method was developed. This technique employs manual, LANDSAT full frame-based wheat or cultivated land proportion estimates from a large number of segments comprising a first sample phase to optimally allocate a smaller phase two sample of computer or manually processed segments. Application to the Kansas Southwest CRD for 1974 produced a wheat acreage estimate for that CRD within 2.42 percent of the USDA SRS-based estimate using a lower CRD inventory budget than for a simulated reference LACIE system. Factor of 2 or greater cost or precision improvements relative to the reference system were obtained.
Thermostabilization System Based on Two-phase Closed Cryogenic Thermosyphon for RED100 Detector
NASA Astrophysics Data System (ADS)
Bolozdynya, A. I.; Efremenko, Yu. V.; Khromov, V. A.; Shafigullin, R. R.; Shakirov, A. V.; Sosnovtsev, V. V.; Tolstukhin, I. A.
The RED 100 emission detector requires thermostabilization at about 100K. The heat transfer characteristics of a two-phase closed cryogenic thermosyphon made of copper pipe and bellow flex hoses with nitrogen fluid have been investigated. The thermosyphon consists of sealed pipe enclosed in a vacuum jacket and uses a free-boiling liquid nitrogen pool as a cooling machine. The system is very flexible and can provide heat transfer rate up to 100 W in the temperature range of 80-100 K.
A Two-Phase Solid/Fluid Model for Dense Granular Flows Including Dilatancy Effects
NASA Astrophysics Data System (ADS)
Mangeney, Anne; Bouchut, Francois; Fernandez-Nieto, Enrique; Narbona-Reina, Gladys
2015-04-01
We propose a thin layer depth-averaged two-phase model to describe solid-fluid mixtures such as debris flows. It describes the velocity of the two phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure, that itself modifies the friction within the granular phase (Iverson et al., 2010). The model is derived from a 3D two-phase model proposed by Jackson (2000) based on the 4 equations of mass and momentum conservation within the two phases. This system has 5 unknowns: the solid and fluid velocities, the solid and fluid pressures and the solid volume fraction. As a result, an additional equation inside the mixture is necessary to close the system. Surprisingly, this issue is inadequately accounted for in the models that have been developed on the basis of Jackson's work (Bouchut et al., 2014). In particular, Pitman and Le replaced this closure simply by imposing an extra boundary condition at the surface of the flow. When making a shallow expansion, this condition can be considered as a closure condition. However, the corresponding model cannot account for a dissipative energy balance. We propose here an approach to correctly deal with the thermodynamics of Jackson's equations. We close the mixture equations by a weak compressibility relation involving a critical density, or equivalently a critical pressure. Moreover, we relax one boundary condition, making it possible for the fluid to escape the granular media when compression of the granular mass occurs. Furthermore, we introduce second order terms in the equations making it possible to describe the evolution of the pore fluid pressure in response to the compression/dilatation of the granular mass without prescribing an extra ad-hoc equation for the pore pressure. We prove that the energy balance associated with this Jackson closure is dissipative, as well as its thin layer associated model. We present several numerical tests for the 1D case that are compared to the
NASA Astrophysics Data System (ADS)
Pettigrew, M. J.; Zhang, C.; Mureithi, N. W.; Pamfil, D.
2005-05-01
Two-phase cross-flow exists in many shell-and-tube heat exchangers. A detailed knowledge of the characteristics of two-phase cross-flow in tube bundles is required to understand and formulate flow-induced vibration parameters such as damping, fluidelastic instability, and random excitation due to turbulence. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures. The array is made of relatively large diameter cylinders (38 mm) to allow for detailed two-phase flow measurements between cylinders. Fiber-optic probes were developed to measure local void fraction. Local flow velocities and bubble diameters or characteristic lengths of the two-phase mixture are obtained by using double probes. Both the dynamic lift and drag forces were measured with a strain gauge instrumented cylinder.
Multi-camera PIV of two-phase oscillating sheet flow
NASA Astrophysics Data System (ADS)
Liu, Chang; Kiger, Ken
2016-11-01
We present a multi-camera thin light sheet imaging method to accurately measure dispersed phase concentration and velocity up to optical densities of close to O [1]. The work is an extension of prior single camera methods that utilize particle image characteristics to identify the dispersed phase and infer the effective measurement volume thickness. By introducing multiple camera perspectives, stereo photogrammetry can be combined with the redundancy of information available in the images to provide 1) increased accuracy in determining individual particle locations, and 2) increased reliability in identifying all of the dispersed phase objects. As a byproduct, the velocity of all three components is also available. As an example, this new method is directly applied to oscillating sheet flow conditions. From a single image pair, individual particles are identified and tracked, giving the instantaneous volume concentration and dispersed phase velocity. A median filter method is used to isolate an image composed only of the much smaller tracer particles, and processed to generate a 3-component continuous phase velocity field. Given the concentration and velocities of the two phases, two-phase flow properties such as the sedimentation rate and momentum coupling will be reported.
Kinetics of amphiphile association with two-phase lipid bilayer vesicles.
Pokorny, A; Almeida, P F; Melo, E C; Vaz, W L
2000-01-01
We examined the consequences of membrane heterogeneity for the association of a simple amphiphilic molecule with phospholipid vesicles with solid-liquid and liquid-liquid phase coexistence. To address this problem we studied the association of a single-chain, fluorescent amphiphile with dimyristoylphosphatidylcholine (DMPC) vesicles containing varying amounts of cholesterol. DMPC bilayers containing 15 mol% cholesterol show a region of solid-liquid-ordered (s-l(o)) coexistence below the T(m) of pure DMPC (23.9 degrees C) and a region of liquid-disordered-liquid-ordered coexistence (l(d)-l(o)) above the T(m). We first examined equilibrium binding and kinetics of amphiphile insertion into single-phase vesicles (s, l(d), and l(o) phase). The data obtained were then used to predict the behavior of the equivalent process in a two-phase system, taking into account the fractions of phases present. Next, the predicted kinetics were compared to experimental kinetics obtained from a two-phase system. We found that association of the amphiphile with lipid vesicles is not influenced by the existence of l(d)-l(o) phase boundaries but occurs much more slowly in the s-l(o) phase coexistence region than expected on the basis of phase composition. PMID:10620291
Development and validation of an X-ray tomograph for two-phase flow.
Hervieu, Eric; Jouet, Emmanuel; Desbat, Laurent
2002-10-01
This paper describes the development and validation of a high spatial resolution X-ray tomograph designed for the investigation of air-water two-phase flow. The device hardware mainly comprises a 60 keV X-ray source, a detector, and an accurate mechanical bench. Our study concentrated on accurate quantification with emphasis on the reconstruction procedure. As is well known, absorption gradients induce reconstruction artifacts when using standard algorithms based on uniform regularization. In the particular case of two-phase flow in a pipe, this leads to poor measurement accuracy in the vicinity of the walls. To overcome such effects, improved algorithms were developed during this study that involve spatially adaptive regularization methods. Preliminary calibration performed on static phantoms clearly exhibited the benefits of the advanced reconstruction algorithms. A validation procedure was carried out on an air-water bubble column, equipped with an optical probe, which could be translated in order to explore the 80 mm x 80 mm square cross section. Comparisons of local void fraction measurements were performed pixel by pixel. They demonstrate the accuracy improvement induced by the advanced reconstruction algorithms.
Oil-water two-phase flow measurement with combined ultrasonic transducer and electrical sensors
NASA Astrophysics Data System (ADS)
Tan, Chao; Yuan, Ye; Dong, Xiaoxiao; Dong, Feng
2016-12-01
A combination of ultrasonic transducers operated in continuous mode and a conductance/capacitance sensor (UTCC) is proposed to estimate the individual flow velocities in oil-water two-phase flows. Based on the Doppler effect, the transducers measure the flow velocity and the conductance/capacitance sensor estimates the phase fraction. A set of theoretical correlations based on the boundary layer models of the oil-water two-phase flow was proposed to describe the velocity profile. The models were separately established for the dispersion flow and the separate flow. The superficial flow velocity of each phase is calculated with the velocity measured in the sampling volume of the ultrasonic transducer with the phase fraction through the velocity profile models. The measuring system of the UTCC was designed and experimentally verified on a multiphase flow loop. The results indicate that the proposed system and correlations estimate the overall flow velocity at an uncertainty of U J = 0.038 m s-1, and the water superficial velocity at U Jw = 0.026 m s-1, and oil superficial velocity at U Jo = 0.034 m s-1. The influencing factors of uncertainty were analyzed.
Thermal instability as a tool to search two-phase regions in centers of galaxies
NASA Astrophysics Data System (ADS)
Rozanska, Agata; Kunneriath, Devaky; Prasad Adhikari, Tek; Czerny, Bozena; Karas, Vladimir
2015-08-01
We show hard radiation, produces in the centers of galaxies, can provide strong clumpiness of the material on distances up to several pc from the black hole. Depending on the shape of this radiation and gas density, thermal instability (TI) can efficiently form two-phase medium, where hot plasma coexists with cold material. Recently, we have made calculations for the conditions appropriate for our Galactic Center considering in particular Minispiral region for which we have studied parameter ranges where the TI may operate.We found that the TI does not operate at the present very low level of the Sgr A* activity. However, Sgr A* was much more luminous in the past.For the highest luminosity states the two-phase medium can be created up to 1.4 pc from the centre, and the cooling/heating timescales are long enough to preserve later the past multi-phase structure. The instability enhances the clumpiness of the mini-spiral medium and creates cold clumps of the order of 1-102 MEarth which may accrete towards Sgr A*.We discuss this mechanism in general case of active galaxies with dense environment.
Two-Phase Wall and Interfacial Friction Forces in Triangle Tight Lattice Rod Bundle Subchannel
NASA Astrophysics Data System (ADS)
Kawahara, Akimaro; Sadatomi, Michio; Shirai, Hiroshi
In order to obtain the data on wall and interfacial friction forces for two-phase flows in a triangle tight lattice subchannel, adiabatic experiments were conducted for single- and two-phase flows under hydrodynamic equilibrium flow conditions. In the experiment, air was used as the test gas, while water and water with a surfactant as test liquids to know the effects of the reduced surface tension on the wall and the interfacial friction forces. The data showed that both the wall and the interfacial friction forces were higher in air-water with a surfactant system than air-water one. In the analysis, the respective data have been compared with the predicted values by existing correlations, and the existing correlations were modified to improve its prediction accuracy against the present data. The modified correlations can predict well the present data on the wall and the interfacial friction forces for both air-water and air-water with a surfactant systems.
Numerical simulation of two-phase flow in horizontal interconnected subchannels
Shourki, M.; Carver, M.B.; Tahir, A.
1985-11-01
Different subchannel computer codes have been successfully used for the thermal-hydraulic analysis of coolant flow in vertical fuel channels. None of these methods, however, is suitable for two-phase flow in horizontal fuel channels, such as those of the CANDU nuclear reactors, due to the lack of appropriate constitutive relationships that can correctly account for the gravity separation effects. A transverse vapor drift model that accounts for the combined effect of gravity separation and turbulent diffusion has been incorporated into the existing subchannel computer code SAGA. Although the basic structure of the code remains similar to SAGA III, some modifications in both the mathematical formulation and numerical solution have been incorporated. These modifications resulted in significant improvements in the code's ability to model horizontal two-phase subchannel flow. The new version of the code was tested and found to be capable of simulating the complex exchange phenomenon between adjacent horizontal subchannels caused by the interaction of turbulent diffusion, pressure gradient, and gravity-induced cross flows. The code predictions were compared with experimental data obtained from two different sources and showed good agreement.
Development of two-phase pipeline hydraulic analysis model based on Beggs-Brill correlation
NASA Astrophysics Data System (ADS)
Waluyo, Joko; Hermawan, Achilleus; Indarto
2016-06-01
The hydraulic analysis is an important stage in a reliable pipeline design. In the implementation, fluid distribution from a source to the sinks often occurs on parallel pipeline networks. The solution to the problem is complicated because of the iterative technique requirement. Regarding its solution effectiveness, there is a need for analysis related to the model and the solution method. This study aims to investigate pipeline hydraulic analysis on distributing of two-phase fluids flow. The model uses Beggs-Brill correlation to converse mass flow rates into pressure drops. In the solution technique, the Newton-Raphson iterative method is utilized. The iterative technique is solved using a computer program. The study is carried out using a certain pipeline network. The model is validated by comparing between Beggs-Brill towards Mukherjee-Brill correlation. The result reveals that the computer program enables solving of iterative calculation on the parallel pipeline hydraulic analysis. Convergence iteration is achieved by 50 iterations. The main results of the model are mass flow rate and pressure drop. The mass flow rate is obtained in the deviation up to 2.06%, between Beggs-Brill and Mukherjee-Brill correlation. On the other hand, the pressure gradient deviation is achieved on a higher deviation due to the different approach of the two correlations. The model can be further developed in the hydraulic pipeline analysis for two-phase flow.
Parasitic Currents in Diffuse-Interface Two-Phase Flow Simulations
NASA Astrophysics Data System (ADS)
Milani, Pedro; Mirjalili, Seyedshahabaddin; Mani, Ali
2016-11-01
Two phase flow phenomena are important in a wide range of applications, such as bubble generation in ocean waves and droplet dynamics in fuel injectors. Several methods can be used to simulate such phenomena. The focus of this study is the diffuse-interface method, in which the interface is described via a mixing energy and spans a few computational cells, while surface tension is modeled as a force density term on the right-hand side of the momentum equation. The advantages of this method include the ability to easily simulate complex geometries since it does not require special treatment around the interface, and to conserve mass exactly. However, this method suffers from parasitic currents, an unphysical velocity field generated close to the interface due to numerical imprecisions in the surface tension term. This can be a serious problem in low speed flows, where the parasitic currents are significant compared to the velocity scale of the problem. In this study, we consider a wide range of diffuse-interface schemes for two-phase flows, including different options for discrete representation of the surface tension force. By presenting an assessment of each method's performance in scenarios involving parasitic currents, we develop accuracy estimates and guidelines for selection among these models. Supported by the ONR.
A consistent projection-based SUPG/PSPG XFEM for incompressible two-phase flows
NASA Astrophysics Data System (ADS)
Liao, Jian-Hui; Zhuang, Zhuo
2012-10-01
In this paper, a consistent projection-based streamline upwind/pressure stabilizing Petrov-Galerkin (SUPG/PSPG) extended finite element method (XFEM) is presented to model incompressible immiscible two-phase flows. As the application of linear elements in SUPG/PSPG schemes gives rise to inconsistency in stabilization terms due to the inability to regenerate the diffusive term from viscous stresses, the numerical accuracy would deteriorate dramatically. To address this issue, projections of convection and pressure gradient terms are constructed and incorporated into the stabilization formulation in our method. This would substantially recover the consistency and free the practitioner from burdensome computations of most items in the residual. Moreover, the XFEM is employed to consider in a convenient way the fluid properties that have interfacial jumps leading to discontinuities in the velocity and pressure fields as well as the projections. A number of numerical examples are analyzed to demonstrate the complete recovery of consistency, the reproduction of interfacial discontinuities and the ability of the proposed projection-based SUPG/PSPG XFEM to model two-phase flows with open and closed interfaces.
Multi-step sequential batch two-phase anaerobic composting of food waste.
Shin, H S; Han, S K; Song, Y C; Lee, C Y
2001-03-01
This study was conducted to evaluate the newly devised process, called MUlti-step Sequential batch Two-phase Anaerobic Composting (MUSTAC). The MUSTAC process consisted of several leaching beds for hydrolysis, acidification and post-treatment, and a UASB reactor for methane recovery. This process to treat food waste was developed with a high-rate anaerobic composting technique based on the rate-limiting step approach. Rumen microorganisms were inoculated to improve the low efficiency of acidogenic fermentation. Both two-phase anaerobic digestion and sequential batch operation were used to control environmental constraints in anaerobic degradation. The MUSTAC process demonstrated excellent performance as it resulted in a large reduction in volatile solids (VS) (84.7%) and high methane conversion efficiency (84.4%) at high organic loading rates (10.8 kg VS m(-3) d(-1)) in a short SRT (10 days). Methane yield was 0.27 m3 kg(-1) VS, while methane gas production rate was 2.27 m3 m(-3) d(-1). The output from the post-treatment could be used as a soil amendment, which was produced at the same acidogenic fermenter without troublesome moving. The main advantages of the MUSTAC process were simple operation and high efficiency. The MUSTAC process proved stable, reliable and effective in resource recovery as well as waste stabilization.
Interface-capturing lattice Boltzmann equation model for two-phase flows
NASA Astrophysics Data System (ADS)
Lou, Qin; Guo, Zhaoli
2015-01-01
In this work, an interface-capturing lattice Boltzmann equation (LBE) model is proposed for two-phase flows. In the model, a Lax-Wendroff propagation scheme and a properly chosen equilibrium distribution function are employed. The Lax-Wendroff scheme is used to provide an adjustable Courant-Friedrichs-Lewy (CFL) number, and the equilibrium distribution is presented to remove the dependence of the relaxation time on the CFL number. As a result, the interface can be captured accurately by decreasing the CFL number. A theoretical expression is derived for the chemical potential gradient by solving the LBE directly for a two-phase system with a flat interface. The result shows that the gradient of the chemical potential is proportional to the square of the CFL number, which explains why the proposed model is able to capture the interface naturally with a small CFL number, and why large interface error exists in the standard LBE model. Numerical tests, including a one-dimensional flat interface problem, a two-dimensional circular droplet problem, and a three-dimensional spherical droplet problem, demonstrate that the proposed LBE model performs well and can capture a sharp interface with a suitable CFL number.
Interface-capturing lattice Boltzmann equation model for two-phase flows.
Lou, Qin; Guo, Zhaoli
2015-01-01
In this work, an interface-capturing lattice Boltzmann equation (LBE) model is proposed for two-phase flows. In the model, a Lax-Wendroff propagation scheme and a properly chosen equilibrium distribution function are employed. The Lax-Wendroff scheme is used to provide an adjustable Courant-Friedrichs-Lewy (CFL) number, and the equilibrium distribution is presented to remove the dependence of the relaxation time on the CFL number. As a result, the interface can be captured accurately by decreasing the CFL number. A theoretical expression is derived for the chemical potential gradient by solving the LBE directly for a two-phase system with a flat interface. The result shows that the gradient of the chemical potential is proportional to the square of the CFL number, which explains why the proposed model is able to capture the interface naturally with a small CFL number, and why large interface error exists in the standard LBE model. Numerical tests, including a one-dimensional flat interface problem, a two-dimensional circular droplet problem, and a three-dimensional spherical droplet problem, demonstrate that the proposed LBE model performs well and can capture a sharp interface with a suitable CFL number.
Device for measuring the liquid portion of a two-phase flow of gas and liquid
Schleimann-Jensen, A.H.
1986-09-02
A device is described for measuring the liquid portion of a two-phase flow of gas and liquid, particularly in conveying a liquid by means of a gas, in which two-phase flow the ratio of mixture between gas and liquid is widely varying. The device consists of a tubular housing and a turbine wheel with axial throw-flow rotatably mounted therein, the turbine wheel being provided with at least one magnetic element at a radially outward portion thereof, the element having limited extent axially and peripherally of the turbine wheel. The device furthermore consists of magnetic pick-up means adapted to emit output signals responsive to the rotary speed of the turbine wheel, the wheel being mounted for axial movement in the direction of flow from an initial position against a biassing force, characterized in that pick-up means are arranged axially spaced along the housing for allowing a measuring of rotary speed of the turbine wheel at various positions of movement within the housing responsive to density as well as speed changes of the flow and hence a determination of the liquid portion thereof by means of a converting device connected to all of the pick-up means. The tubular housing preferably is mounted vertically with the turbine wheel in its initial position being located lowermost.
Multiphysics modeling of two-phase film boiling within porous corrosion deposits
NASA Astrophysics Data System (ADS)
Jin, Miaomiao; Short, Michael
2016-07-01
Porous corrosion deposits on nuclear fuel cladding, known as CRUD, can cause multiple operational problems in light water reactors (LWRs). CRUD can cause accelerated corrosion of the fuel cladding, increase radiation fields and hence greater exposure risk to plant workers once activated, and induce a downward axial power shift causing an imbalance in core power distribution. In order to facilitate a better understanding of CRUD's effects, such as localized high cladding surface temperatures related to accelerated corrosion rates, we describe an improved, fully-coupled, multiphysics model to simulate heat transfer, chemical reactions and transport, and two-phase fluid flow within these deposits. Our new model features a reformed assumption of 2D, two-phase film boiling within the CRUD, correcting earlier models' assumptions of single-phase coolant flow with wick boiling under high heat fluxes. This model helps to better explain observed experimental values of the effective CRUD thermal conductivity. Finally, we propose a more complete set of boiling regimes, or a more detailed mechanism, to explain recent CRUD deposition experiments by suggesting the new concept of double dryout specifically in thick porous media with boiling chimneys.
Ionic liquid-based aqueous two-phase system extraction of sulfonamides in milk.
Shao, Mingyuan; Zhang, Xuli; Li, Na; Shi, Jiayuan; Zhang, Huijie; Wang, Zhibing; Zhang, Hanqi; Yu, Aimin; Yu, Yong
2014-06-15
A simple method for the determination of six sulfonamides (SAs) in milk samples was developed. 1-Butyl-3-methylimidazolium tetrafluoroborate and trisodium citrate dihydrate were used to form aqueous two-phase system. The aqueous two phase system was applied to the extraction of the SAs and the determination of the analytes was performed by high-performance liquid chromatography. To achieve optimum extraction performance, several experimental parameters, including the type and the amount of salt, the type and amount of ionic liquid, ultrasonic time and pH of sample solution, were investigated and optimized. Under the optimal experimental conditions, good linearity was observed in the range of 8.55-1036.36ngmL(-1). The limits of detection and quantification were in the range of 2.04-2.84 and 6.73-9.37ngmL(-1), respectively. The present method was successfully applied to the determination of SAs in milk samples, and the recoveries of analytes were in the range of 72.32-108.96% with relative standard deviations ranging from 0.56 to 12.20%. The results showed that the present method was rapid, feasible and environmentally friendly.
Vertical two-phase flow regimes and pressure gradients: Effect of viscosity
Da Hlaing, Nan; Sirivat, Anuvat; Siemanond, Kitipat; Wilkes, James O.
2007-05-15
The effect of liquid viscosity on the flow regimes and the corresponding pressure gradients along the vertical two-phase flow was investigated. Experiment was carried out in a vertical transparent tube of 0.019 m in diameter and 3 m in length and the pressure gradients were measured by a U-tube manometer. Water and a 50 vol.% glycerol solution were used as the working fluids whose kinematic viscosities were 0.85 x 10{sup -6} and 4.0 x 10{sup -6} m{sup 2}/s, respectively. In our air-liquid annular two-phase flow, the liquid film of various thicknesses flowed adjacent to the wall and the gas phase flowed at the center of the tube. The superficial air velocity, j{sub air}, was varied between 0.0021 and 58.7 m/s and the superficial liquid velocity, j{sub liquid}, was varied between 0 and 0.1053 m/s. In the bubble, the slug and the slug-churn flow regimes, the pressure gradients decreased with increasing Reynolds number. But in the annular and the mist flow regimes, pressure gradients increased with increasing Reynolds number. Finally, the experimentally measured pressure gradient values were compared and are in good agreement with the theoretical values. (author)
Single- and Two-Phase Flow Characterization Using Optical Fiber Bragg Gratings
Baroncini, Virgínia H.V.; Martelli, Cicero; da Silva, Marco José; Morales, Rigoberto E.M.
2015-01-01
Single- and two-phase flow characterization using optical fiber Bragg gratings (FBGs) is presented. The sensor unit consists of the optical fiber Bragg grating positioned transversely to the flow and fixed in the pipe walls. The hydrodynamic pressure applied by the liquid or air/liquid flow to the optical fiber induces deformation that can be detected by the FBG. Given that the applied pressure is directly related to the mass flow, it is possible to establish a relationship using the grating resonance wavelength shift to determine the mass flow when the flow velocity is well known. For two phase flows of air and liquid, there is a significant change in the force applied to the fiber that accounts for the very distinct densities of these substances. As a consequence, the optical fiber deformation and the correspondent grating wavelength shift as a function of the flow will be very different for an air bubble or a liquid slug, allowing their detection as they flow through the pipe. A quasi-distributed sensing tool with 18 sensors evenly spread along the pipe is developed and characterized, making possible the characterization of the flow, as well as the tracking of the bubbles over a large section of the test bed. Results show good agreement with standard measurement methods and open up plenty of opportunities to both laboratory measurement tools and field applications. PMID:25789494
Purification of Active Myrosinase from Plants by Aqueous Two-Phase Counter-Current Chromatography
Wade, Kristina L.; Ito, Yoichiro; Ramarathnam, Aarthi; Holtzclaw, W. David; Fahey, Jed W.
2014-01-01
Introduction Myrosinase (thioglucoside glucohydrolase; E.C. 3.2.1.147), is a plant enzyme of increasing interest and importance to the biomedical community. Myrosinase catalyses the formation of isothiocyanates such as sulforaphane (frombroccoli) and 4-(α-l-rhamnopyranosyloxy)benzyl isothiocyanate (from moringa), which are potent inducers of the cytoprotective phase-2 response in humans, by hydrolysis of their abundant glucosinolate (β-thioglucoside N-hydroxysulphate) precursors. Objective To develop an aqueous two-phase counter-current chromatography (CCC) system for the rapid, three-step purification of catalytically active myrosinase. Methods A high-concentration potassium phosphate and polyethylene glycol biphasic aqueous two-phase system (ATPS) is used with a newly developed CCC configuration that utilises spiral-wound, flat-twisted tubing (with an ovoid cross-section). Results Making the initial crude plant extract directly in the ATPS and injecting only the lower phase permitted highly selective partitioning of the myrosinase complex before a short chromatography on a spiral disk CCC. Optimum phase retention and separation of myrosinase from other plant proteins afforded a 60-fold purification. Conclusion Catalytically active myrosinase is purified from 3-day broccoli sprouts, 7-day daikon sprouts, mustard seeds and the leaves of field-grown moringa trees, in a CCC system that is predictably scalable. PMID:25130502
NASA Astrophysics Data System (ADS)
Bar-Cohen, Avram; Sheehan, Jessica R.; Rahim, Emil
2012-01-01
A comprehensive literature review and analysis of recent microchannel/microgap heat transfer data for two-phase flow of refrigerants and dielectric liquids is presented. The flow regime progression in such a microgap channel is shown to be predicted by the traditional flow regime maps. Moreover, Annular flow is shown to be the dominant regime for this thermal transport configuration and to grow in importance as the channel diameter decreases. The results of heat transfer studies of single miniature channels, as well as the analysis and inverse calculation of IR images of a heated microgap channel wall, are used to identify the existence of a characteristic M-shaped heat transfer coefficient variation with quality (or superficial velocity), with inflection points corresponding to transitions in the two-phase cooling modalities. For the high-quality, Annular flow conditions, the venerable Chen correlation is shown to yield predictive agreement for microgap channels that is comparable to that attained for macrochannels and to provide a mechanistic context for the thermal transport rates attained in microgap channels. Results obtained from infrared imaging, revealing previously undetected, large surface temperature variations in Annular flow, are also reviewed and related to the termination of the favorable thin-film evaporation mode in such channels.
Volume-Of-Fluid Simulation for Predicting Two-Phase Cooling in a Microchannel
NASA Astrophysics Data System (ADS)
Gorle, Catherine; Parida, Pritish; Houshmand, Farzad; Asheghi, Mehdi; Goodson, Kenneth
2014-11-01
Two-phase flow in microfluidic geometries has applications of increasing interest for next generation electronic and optoelectronic systems, telecommunications devices, and vehicle electronics. While there has been progress on comprehensive simulation of two-phase flows in compact geometries, validation of the results in different flow regimes should be considered to determine the predictive capabilities. In the present study we use the volume-of-fluid method to model the flow through a single micro channel with cross section 100 × 100 μm and length 10 mm. The channel inlet mass flux and the heat flux at the lower wall result in a subcooled boiling regime in the first 2.5 mm of the channel and a saturated flow regime further downstream. A conservation equation for the vapor volume fraction, and a single set of momentum and energy equations with volume-averaged fluid properties are solved. A reduced-physics phase change model represents the evaporation of the liquid and the corresponding heat loss, and the surface tension is accounted for by a source term in the momentum equation. The phase change model used requires the definition of a time relaxation parameter, which can significantly affect the solution since it determines the rate of evaporation. The results are compared to experimental data available from literature, focusing on the capability of the reduced-physics phase change model to predict the correct flow pattern, temperature profile and pressure drop.
Multistage aqueous two-phase extraction of a monoclonal antibody from cell supernatant.
Muendges, Jan; Zalesko, Alexej; Górak, Andrzej; Zeiner, Tim
2015-01-01
This article presents results of continuous multistage aqueous two-phase extraction of an immunoglobulin G1 from cell supernatant in a mixer-settler unit. An aqueous two-phase system consisting of polyethylene glycol 2000, phosphate salt, and water was applied without and with sodium chloride (NaCl). Influences of different parameters such as throughput, phase ratio, and stage number on the extraction performance were analyzed. For systems without NaCl, the extraction was carried out as a washing step. An increase of stage number from one to five stages enabled to increase the immunoglobulin G1 purity from 11.8 to 32.6% at a yield of nearly 90%. Furthermore, a reduction of product phase volume due to a higher phase ratio led to an increase of purity from 20.8 to 29.6% in a three-stage countercurrent extraction. For experiments with NaCl moderate partitioning conditions were adjusted by adding 8 wt% NaCl. In that case, the extraction was carried out as a stripping step.
Continuous aqueous two-phase extraction of human antibodies using a packed column.
Rosa, P A J; Azevedo, A M; Sommerfeld, S; Bäcker, W; Aires-Barros, M R
2012-01-01
The performance of a pilot scale packed differential contactor was evaluated for the continuous counter-current aqueous two-phase extraction (ATPE) of human immunoglobulin G (IgG) from a Chinese hamster ovary (CHO) cells supernatant (CS) enriched with pure protein. Preliminary studies have been firstly performed in order to select the dispersed phase (phosphate-rich or polyethylene glycol 3350 Da (PEG)-rich phase) and the column packing material. The PEG-rich phase has been selected as the dispersed phase and the stainless steel as the preferred material for the column packing bed since it was not wetted preferentially by the selected dispersed phase. Hydrodynamic studies have been also performed, and the experimental results were successfully adjusted to the Richardson-Zaki and Mísek equations, typically used for the conventional organic-aqueous two-phase systems. An experimental set-up combining the packed column with a pump mixer-settler stage showed to have the best performance and to be advantageous when compared to the IgG batch extraction. An IgG recovery yield of 85% could be obtained with about 50% of total contaminants and more than 85% of contaminant proteins removal. Mass transfer studies have revealed that the mass transfer was controlled by the PEG-rich phase. A higher efficiency could be obtained when using an extra pump mixer-settler stage and higher flow rates.